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THE 



MECHANICAL ENGINEERING 



OF 



POWER PLANTS. 



'V 

FREDERIC REMSEN HUTTON, E.M, Ph.D., 

Professor of Mechanical Engineering in the 
School of Engineering of Columbia University. 



FIRST EDITION-, 
FIRST THOUSAND. 



1i^ 



'\' 0'3^/i5.ft 



^^^].^r*^''''im. 



^?::n 



NEW YORK: 

JOHN WILEY & SONS. 

London: CHAPMAN & HALL, Limited. 

1897. 



(5/ 



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Uv 



Copyright, 1897, 

BY 

F. R, HUTTON. 



\ 



h 



K 



As 







ROBERT DRUMMOND, ELECTROTYPHR AND PRINTER, NEW YORK. 



PREFACE 



This book has been undertaken with two distinct objects 
in view, and according to a principle suggested by these 
objects. 

The first and primary intention is to provide a book to 
serve as a text-book in class-room work in a University which 
makes the education of engineers a part of its duty. This 
object has given the book its form and has determined its 
arrangement. 

It must have been observed by every instructor that the 
most enthusiastic class of students who follow engineering in 
the schools are those who have had a previous experience in 
the shop or in the power house which has made them familiar 
with the conditions which there prevail, and has brought to 
their attention questions for which they have sought to find 
answers. It is the wish of its projector that, so far as that 
condition can be met by any book whatever, this book should 
put all students of engineering somewhat upon the footing 
of these fortunate persons. It must therefore present the 
machinery and appliances of the power house before the 
reader's mind from the practical or experimental side, and 
make him familiar with the power plant in its various forms, 
and seek to familiarize him with the solutions which experi- 
ence and good judgment have proposed for problems of this 
sort. 

It is believed that with this knowledge and with the train- 
ing in the weighing of advantages and disadvantages which 
attach to any given solution the student is most satisfactorily 
fitted to take up as a later feature of his engineering study 
those principles of mechanics, physics, and thermodynamics 
upon which all successful practice must ultimately rest. If 
he is prepared by the practical and experimental treatment 



IV PREFA CE, 

first, he is more r&ady to appreciate the significance of the 
abstract and theoretical considerations which belong to the 
truly professional departments of engineering. 

It is believed furthermore that this principle is a sound one 
and calculated to lead to the best results. If the beginning 
is made with general principles and fundamental theories, and 
their application made to come afterwards in an apparently 
secondary relation to the principles, a habit of mind is engen- 
dered which is dangerous to a wise application of theory to 
practice in early professional life. The temptation is to make 
practice square with the rational or transcendental depart- 
ments of theory rather than to see in every illustration of suc- 
cessful practice the application of a sound theory which took 
account both of the experimental and the rational practice. 
May not this be one reason why inexperienced graduates 
have disappointed in the past both themselves and those who 
have sought to use and employ them? Their school-training 
from its point of view had unfitted them for the point of view 
which in life they must occupy. It is the case that in most 
departments of learning other than engineering, the method 
which has been found most satisfactory is the rise from the 
concrete and the object to the abstract and the principle. 

With this end in view, it will be understood that this 
book is not intended to be a complete treatise upon the power 
plant, but solely upon that department which for the time 
being may be called '* the mechanical engineering " of the 
power plant, as distinguished from the dynamical engineering 
of the power plant, which would rightly and properly form a 
second and further department of the subject. In that view 
the mathematical form has been avoided with intention almost 
throughout, and furthermore the tempting allurements to 
wander in the fields of design have been resisted in the main. 
It is felt that the subject of design might properly be based 
upon such knowledge as this treatise aims to impart, but be- 
longs to a further stage of development and observation, and 
should receive a treatment from that other point of view 
which it has received from certain masters. That it might be 



PREFA CE. V 

apparent, however, for student use that the book was only 
a foundation and not a complete and exhaustive discussion, 
considerable material has been thrown in the form of notes as 
appendices, which are to stand as open doors from the various 
chapters and subdivisions of the book through which the 
student may move onward for distinctly professional study if 
so inclined. References are also freely introduced in these 
appendices as a means of stimulating further and more ad- 
vanced study. In class-room use it is intended to make use 
of much other and fuller illustration of detail by photograph, 
lantern-slide, and drawing, so that it has not been thought 
possible or advisable to try and include every variant from 
usual forms. Growth, change, and improvement must also 
be met by such supplementary illustrations. 

The second object has been to furnish a compact view of 
power-house practice which should serve for a group of per- 
sons, both students and others, to whom the problems of 
design were foreign and undesired, and yet who would appre- 
■ciate a non-mathematicl treatment of the problem as a whole. 
The power house occupies in the industrial and business 
atmosphere of this period an importance which it never 
has had hitherto, and the success of business enterprises and 
manufacturing corporations is often bound up in the satisfac- 
tory condition of their power house. It is desired to enable 
persons in responsible relations to it to derive something of 
benefit and information of the same sort which is necessary to 
those who are employed under them in the power house, so 
that they may be able to judge fairly of the soundness of 
opinions which may be offered upon power-house questions. 

Such persons also are those who as graduates from tech- 
nical schools go to positions of responsibility and trust involv- 
ing power problems, and yet for whom the masterly treatises 
on design and construction which have been hitherto written 
would either be too voluminous, because they contained much 
of valuable material which was of no use to them, or would 
not meet the needs of the case, because they viewed the 
problems from a different standpoint. 



VI PREFA CE. 

In this view it is not to be considered that there is much 
of original or created material to be found in the book, for 
the reason that to have been original would have frustrated 
its purpose. It will further appear that much of it is simple. 
It will be a pleasure to find that the arrangement of the 
material shall have been sufficiently novel and convenient to 
justify its being cast in this form, and if the apparent sim- 
plicity shall have resulted from a successful attempt to make 
clear the sometimes complicated matters in question. 

It is impossible at this late day to present anything which 
may not have been presented by some one else hitherto, but 
the obligations of the writer are particularly to be expressed 
to Professor R. H. Thurston and Mr. Jay M. Whitham for 
the kindly permission to make use of illustrations which had 
already served them, and in the department of boilers to the 
Hartford Steam Boiler Insurance and Inspection Company, 
through whose president, Mr. Jeremiah M. Allen, permission 
was obtained to present illustrative material which they had 
prepared as the result of many years' experience in the inspec- 
tion and improved construction of the various types of shell 
boilers. Many makers and builders of engines and power- 
house appliances have also been most courteous in permitting 
use of illustrations. 

It is not the modern custom to dedicate a book to an indi- 
vidual. This one will be recognized, however, by a number 
of practising engineers as being the embodiment and an 
extension of the course in Engines and Boilers which has 
been for many years a feature of a relation which the author 
has found particularly agreeable. For this reason, if any- 
thing like a dedication were permitted him, it would be to the 
body of graduates in engineering from an American Technical 
School, the memory of whose interest in the subject and 
whose cordial cooperation and earnestness in its development 
in the classroom have made the preparation of this practical 
treatise a pleasure and a privilege. 

F. R. HUTTON. 
Columbia University, New York. 
January, 1897. 



TABLE OF CONTENTS, 



CHAPTER I. . 

INTRODUCTORY, 

PAK. PAGE 

1. Sources of Motor Energy , i 

2. Analysis of Development of a Power Plant. , 3 

3. Units of Output in a Power Plant 4 

4. Measurement of Output 5 

5. The Scheme of Classification 5 

PART I. 

CHAPTER II. 

THE MECHAl^ISM OF ENGINES. 

6. The Horse-power of a Cylinder 7 

7. " " " " the Resistance 8 

8. Transformations of the Horse-power Formula g 

9. Essential Parts of a Typical Reciprocating Steam-engine 9 

10. General Features of the Typical Engine Mechanism ii 

11. Length of the Typical Reciprocating Engine 17 

12. Oscillating Engine 17 

13. Trunk-engine 2a 

14. Back-acting Engine 23 

15. Engines Classified by Arrangement of Cylinder-axis 26 

16. Horizontal Engine 26 

17. Vertical Engine 31 

18. Inverted Vertical Engine 33 

19. Direct Vertical Engine 36 

20. Inclined Engine 36 

21. Combined Horizontal and Vertical Engines 40 

22. Direct-acting and Beam Engines 41 

23. Beam-engines ... 42 

24. Structure of Beam-engines 43 

25. Objections to the Beam-engine. Side-lever Engine 49 

26. The Rotary Steam-engine 52 



VIU TABLE OF CONTENTS. 

PAR. PAGE 

H'j. Rotary Steam-engines in which Pistons and Abutment alternate 

their Functions 54 

^8. Rotary Steam-engine with Persistent Functions of Piston and 

Abutment 57 

29. Advantages of the Rotary Engine 59 

30. Disadvantages of the Rotary Engine 60 

31. The Steam Turbine 61 

32. Square-piston Engines and Disk Engines . 61 

33. Sundry Special Mechanisms 66 

CHAPTER III. 
ENGINES CLASSIFIED BY USE OF STEAM. 

34. Introductory 70 

35. High-speed Engines 70 

36. Low-speed Engines 71 

37. Piston-speed in Feet per Minute 72 

38. Double- and Single-acting Engines 73 

39. The Cornish Engine 73 

46. Operation of the Cornish-engine Cylinder 74 

41. Cataract of the Cornish Pumping-engine 75 

42. Advantages and Disadvantages of the Cornish Pumping-engine... 76 

43. Single-acting Rotative Engines 77 

44. Expansive and Non-expansive Working of Engines 79 

CHAPTER IV. 
CONDENSING AND NON-CONDENSING ENGINES. 

45. Introductory c 85 

46. Advantages of the Condensing Engine 87 

47. Disadvantages of the Condensing Engine 89 

48. The Condenser of a Condensing Engine 91 

49. Jet and Surface Condensers 97 

50. The Cold-well 97 

51. The Air-pump and Foot-valve 99 

52. The Circulating-pump 102 

53. The Independent Air-pump 103 

54. The Gravity Condenser 105 

55. The Siphon or Injector Condenser 106 

56. The Ejector Condenser with Pump 109 

57. The Exhaust-steam Ejector Condenser iii 

58. Pump Condensers 112 

59. The Hot-well 114 

60. The Feed-pump 115 

CHAPTER V. 

SIMPLE AND CONTINUOUS-EXPANSION ENGINES. 

61. Introductory 116 

62. Action of Steam in Compound Engines 118 



TABLE OF CONTENTS, IX 

PAR. PAGE 

6.3. Mechanisms of the Compound Engine 120 

64. Beam Compound Engines 125 

65. Diagram of Steam-effort in a Compound Engine 125 

66. Arrangement of Cylinders in Multiple-expansion Engines 131 

67. Reheaters in Compound Engines 131 

68. Compounding above the Atmosphere 134 

69. Compound Locomotives 137 

70. Advantages of the Compound Engine 139 

71. Disadvantages of the Compound Engine. 141 

72. Proportions of Compound-engine Cylinders 142. 



CHAPTER VI. 

SUNDRY CLASSIFICATIONS. CONTROL OF ENERGY, 

73. Review and Introductory 144 

74. Control of Energy of the Steam in an Engine. Throttling-engines.. 145 

75. Cut-off Regulation of a Steam-engine. Cut-off Engines 147 

76. Advantages and Disadvantages of the Throttling^engine 148 

77. " " " " " Cut-off Engine 15a 

78. Summary and Conclusions , , 152 

CHAPTER VII. 

VALVES AND VALVE-GEARING, 

79. Introductory 153, 

80. Three-way and Four-way Cock Valves 154 

8i. Plain Slide-valve. Working Full Stroke 157 

82. The Eccentric is a Crank . 159, 

83. Setting of a Plain Slide-valve Working Non-expansively 161 

84. The B Valve 163. 

85. Lap in the Slide-valve 164. 

86. Effects of Lap 165 

87. Inside Lap i66- 

88. Effects of Inside Lap 166 

89. Exhaust-clearance -. 167 

90. Lead in the Slide-valve 16S 

91. Effects of Lead 169. 



CHAPTER VIII. 

VALVE-GEARING, CONTINUED. 

92. Setting of Slide-valve without Access to Valve-chest. Setting by 

Sound 170 

93. Motion-curves for Slide-valves 172 

94. The Zeuner Polar Diagram for Slide-valves 176 



X TABLE OF CONTENTS. 

PAR. PAGE 

95. Use of the Zeuner Polar Diagram 180 

96. Valve-gear Problems and Design 181 

97. Limitations of the Single Slide-valve 183 

98. Valve-gear for High Degrees of Expansion. Two-valve System-. 184 

99. Three- and Four-valve Gears 188 



CHAPTER IX. 

VALVE-GEARING, CONTINUED. 

100. Shortening Steam-passages 189 

loi. " the Throw of the Valve. Allen Valve 191 

102. Gridiron Slide-valve 192 

103. Balancing Slide-valves. Piston-valves 193 

104. Pressure-plate Systems 196 

105. Valves Taking Steam Internally 201 

106. ' ' with Counter-pressure 201 

307. Poppet-valves 202 

CHAPTER X. 

CAM AND RELEASE VALVE-GEARS. 

108. Cam Valve-gears 204 

109. Trip or Releasing Valve-gears - 210 

no. Corliss Valve-gears 211 

111. Advantages of Trip Valve-gear 215 

112. Disadvantages of Trip Valve-gear 215 

113. Steam-thrown Valves ,....,... 216 



CHAPTER XI. 

REVERSING VALVE-GEARS. LINK-MOTIONS. 

114. Reversing-gears with One Eccentric 220 

115. " " " Two Eccentrics. Gab-hooks 222 

116. Link-motion of Howe or Stephenson. 223 

117. Features of the Stephenson Link-motion 225 

118. Gooch's Link-motion 227 

119. Allan's Link-motion 228 

120. Radial Valve-gear. Joy's Valve-gear 228 

121. Walschaert Valve-gear 230 

122. Brown. Marshall, Hackworth, and Angstrom Valve-gears 231 

123. Allen Link-motion 232 

124. Link-motions for Riding Cut-off-valves 233 

125. Power Reversing-gears 233 



TABLE OF CONTENTS, XI 



CHAPTER XII. 

VA RIA BLE-CUT-OFF VALVE GEARS. 

PAR PAGE 

126. Introductory. 235 

127. Cut-off Varies by Varying Throw of Valve. 235 

128. " ■' *' " Lap of Valve 236 

129. *■ " " *' Angular Advance of Eccentric 239 

130. " " ** '* Point of Release or Trip 240 



CHAPTER XIII. 

GOVERNORS FOR STEAM-ENGINES. 

T31. Introductory 241 

132. Classifications of Governors 243 

133. Fly-ball or Watt Conical-pendulum Governor 245 

134. Theory of the Watt Governor 246 

135. Defects of the Fly-ball Governor 247 

136. Loaded Governors • , 247 

137. Parabolic-governor 249 

138. Balanced Governor without Spring 251 

139. Balanced or Spring Governors 253 

140. Shaft-governors. 254 

141. Inertia-governors 256 

142. Spindle- and Shaft-governors Compared 258 

143. Resistance-governors 258 

144. Electromagnetic Governors- 260 

145. Dynamometric Governors 261 

146. Safety-stops 262 

147. Marine-engine Governors. 263 

148. Connections of Governor to Control Engine 264 



CHAPTER XIV. 

ENGINE FOUNDATIONS AND BED-PLATES. 

149. Introductory 265 

150. The Bed-plate of a Horizontal Engine 265 

151. The Bed or Frame of a Vertical Engine 271 

152. The Foundation of an Engine . 273 

153. Construction of Engine-foundations 275 

154. Footings to Prevent Vibration 276 

155. Foundation- bolts 278 

156. Alignment of Foundation Template 280 

157. Locating the Bed plate on the Foundation 281 

158. Alignment of the Outer Pillow-block or Shaft-bearing 283 



XU TABLE OF CONTENTS, 



CHAPTER XV. 

CYLINDER, PISTON, AND PISTON-ROD. 

PAR. PAGE 

159. The Cylinder-casting 287 

160. The Counterbore 289 

161. Cylinder-cocks and Snifting-valves 290 

162. The Cylinder-jacket or Lagging 291 

163. The Structure of the Piston . 293 

164. The Piston-packing 295 

165. The Piston-rings 297 

166. The Piston-rod 302 

167. The Stuffing-box 305 

168. Air-valves 310 

CHAPTER XVI. 

CROSS-HEAD. GUIDES. CONNECTING-ROD. 

169. The Guides or Slides 311 

170. The Cross-head 314 

171. The Cross-head Pin or Wrist-pin 319 

172. Parallel Motions 319 

173. The Connecting-rod 320 

174. The Stub End . 321 

175. Forked-end Connecting-rod. Double Rods 327 

CHAPTER XVII. 

CRANK. SHAFT. ECCENTRIC. FLY-WHEEL, 

176. The Crank-shaft 329 

177. The Crank-pin 330 

178. The Crank 332 

179. The Locomotive Crank and Shaft 334 

180. The Marine Crank-shaft 335 

181. The Main or Crank Bearing 337 

182. The Eccentric 340 

183. The Eccentric-rod and Valve-stem 341 

184. The Fly-wheel 342 

185. The Strains in Fly-wheels 344 

186. Solid and Segmental Fly-wheels 345 

187. Fly-band-wheels 348 

188. Composite Band-wheels 348 

189. Conclusions and General 348 

CHAPTER XVIII. 

PIPING FOR THE ENGINE AND ITS ATTACHMENTS, 

190. General. Throttle-valve 350 

191. Steam-pipe 351 



TABLE OF CONTENTS. Xlll 

PAR. PAGE 

192. Expansion of Steam-pipe. Expansion-joints and Hanging 354 

193. Grading of Steam- pipe 356^ 

194. Drainage of Steam-pipe 357 

195. Non-conducting Coverings 362 

196. Exhaust-pipe 363 

197. Oil-extractors 365, 

198. Drip-connections 368 

199. Sundry Connections and Attachments 369. 

200. Summary 369. 



PART II. 

CHAPTER XIX. 
THE STEAM-BOILER. GENERAL CONSTRUCTION. 

2or. Introductory 370 

202. Shapes for Steam-boilers 370 

203. Materials for Steam-boilers, Copper and Cast Iron 371 

204. Wrought-iron and Steel Boilers 374 

205. Steel Boilers 376 

206. Testing of Boiler-plate 378 

207. Thickness of Boiler-plate 378 

208. Curving of Plates for Shells 380 

209. Arrangement of Rings of Plate in Shells 383 

210. Heads of Boiler-shells. Flanging , 385 

211. Joints in Boiler-shells. Welding 387 

212. Riveted Joints for Boiler-shells 389. 

213. Construction of a Riveted Joint. Punching and Drilling 39a 

214. Punching and Drilling Compared 392 

215. Hand- and Machine-riveting 395 

216. Design of a Riveted Joint. Strength 39^ 

217. Rivets and their Arrangement 40a 

218. Failure of a Riveted Joint 405 

219. The Drift-pin 406 

220. Stays and Staying 407 

221. Manholes 416 

222. Hand-holes 419 

223. Edge-planing and Calking 419 

224. Sundry Details of Construction 419 

CHAPTER XX. 

TYPES OF BOILERS. EXTERN ALLY-FIRED SHELL BOILERS. 

225. Classification of Types , 421 

226. Plain Cylinder-boiler 422 



XIV TABLE OF CONTENTS, 

PAR. PAGE 

227. Domes and Steam -drums 425 

228. Conditions suggesting the Use of the Plain Cylinder-boiler. 433 

229. Objections to the Cylinder-boiler 434 

230. The Elephant, French, or Union Boiler 434 

231. The Mud-drum 437 

232. The Cylinder Flue-boiler 43^ 

233. Uses and Application of the Cylinder Flue-boiler 444 

234. The Cylinder Tubular or Multitubular Boiler 444 

235. Boiler- tubes 445 

236. Ribbed Tubes. Serve-tubes. Retarders 446 

237. Expanding of Tubes 446 

238. Staying of Tubular and Flue Boilers 449 

239. Uses and Application of the Cylinder Tubular Boiler 449 

CHAPTER XXI. 

TYPES OF BOILERS. EXTERNALLY-FIRED SECTIONAL BOILERS. 

240. Definition of a Sectional Boiler 451 

241. Advantages of the Sectional Principle 451 

242. Disadvantages of the Sectional Principle 453 

243. Classes of Sectional Boiler 455 

244. Spherical Unit Type 458 

245. Vertical Tubular Type. .. 460 

246. Horizontal Straight Tubular Type , 460 

247. Closed-tube Types. Field Tubes 464 

248. Bent- or Curved-tube Types 468 

249. Sundry Types of Externally-fired Boiler 470 

CHAPTER XXII. 
TYPES OF BOILERS. INTERNALLY-FIRED SHELL BOILERS, 

250. Internally-fired Boilers. General 471 

251. Cornish and Lancashire Boilers , . . 473 

252. The Galloway Boiler 474 

253. The Scotch or Cylindrical Marine Boiler 477 

254. The Rectangular Marine Boiler (Martin Boiler) 480 

255. The Typical Locomotive Boiler 482 

256. Modifications of the Locomotive Boiler 486 

257. The Upright Boiler 490 

258. Modifications of the Upright Boiler 492 

259. The Fire-engine Boiler 495 

CHAPTER XXIII. 

TYPES OF BOILERS. INTERNALLY-FIRED SECTIONAL BOILERS. 

260. General 498 

261. The Water-tube Boiler 498 



TABLE OF CONTENTS, XV 



262. The Coil-boiler 499 

^63. Sundry Types. Conclusion 502 



CHAPTER XXIV. 

BOILER-SETTINGS, 

264. General. Side Walls 504 

265. Buck-stays and Tie-rods 505 

266. Hanging of Boilers 508 

267. Boiler-fronts 5 10 

268. The Dead-plate and Mouthpiece of the Furnace 516 

269. The Ash-pit 518 

270. The Furnace 520 

271. The Grate-bars. Stationary Grates , 521 

272. Shaking and Dumping Grate-bars 525 

273. Step-grates 527 

274. Mechanical or Travelling Grates 529 

275. Mechanical Stokers 530 

276. Inclined and Horizontal Grates 535 

277. The Bridge-wall 538 

^78. The Combustion-chamber 543 

279. The Back Connection 545 

^80. The Front Connection 546 

281. The Flue to the Chimney-stack 546 

282. The Damper and Damper Regulator 548 

283. The Chimney 551 

284. Artificial Draft - 553 

285. Advantages of Artificial Draft 7, 554 

286. Disadvantages of Artificial Draft 555 



CHAPTER XXV. 

THE BOILER-FURNACE AS THE ORIGIN OF POWER, 

287. Calorific Power of a Fuel 557 

288. Force corresponding to the Combustion of One Pound of Fuel.. ..... 559 

289. Heat of Combustion in the Furnace. 560 

290. Pounds of Coal Burned per Square Foot of Grate 560 

291. Pounds of Water per Pound of Coal Burned 562 

292. ** " " " Horse-power per Hour 563 

293. Transfer of Heat 564 

294. Ratio of Grate-surface to Heating-surface 565 

295. Evaporation per Square Foot of Heating-surface 566 

296. Pounds of Air required per Pound of Coal , 567 

297. Oil as Fuel 567 

298. Advantages of Boiler-firing with Oil , 568 



XVI TABLE OF CONTENTS, 

PAR. PAGff 

299. Disadvantages of Boiler-firing with Oil 56^ 

300. Gas as Fuel , 570 

301. Smoke-prevention 573 



CHAPTER XXVI. 
BOILER ACCESSORIES AND APPLIANCES. 

302. Introductory , 57S 

303. Steam-gauge 578. 

304. Standardization or Calibration of Steam-gauges 581 

305. Recording-gauges 582 

306. Water-gauges. 582 

307. The Glass Water-gauge and Column-pipe 583 

308. The Gauge-cocks 587 

309. Float Water-gauges 589 

310. Low-water Alarms 589 

'311. Fusible or Safety Plugs 590 

312. Introduction of the Feed- water 591 

313. The Feed-pipe and Feed-valves 592 

314. The Supply of Feed-water to the Boiler 593 

315. The Fly-wheel Pump 595 

316. The Direct-acting Pump 596 

317. The Injector ■. 599 

318. The Handling of the Injector 6oa 

319. Advantages and Disadvantages of the Injector 602 

320. The Economy of Preheating the Feed- water 603 

321. Exhaust-steam Heaters 603 

322. Flue-heaters or Economizers 605 

323. Automatic Feeding Apparatus 609 

324. The Blow-off Valve 610 

325. The Safety-valve , 611 

326. Forms of Safety-valve 612 



CHAPTER XXVII. 

CARE AND MANAGEMENT OF BOILERS, 

327. Firing ^ 616 

328. Cleaning Fires 617 

329. Banking Fires 617 

330. Regulation of the Fire and Pressure of Steam 618 

33T. Cleaning the Heating-surface Outside 61& 

332. Boiler-scale or Incrustation 619. 

333. Inconveniences due to Boiler-scale 622 

334. Removal of Boiler-scale 623 

335. Prevention of Scale-formation 625, 



TABLE OF CONTENTS, XVll 

a»AR. PAGE 

336. Previous Purification of Feed- water 626 

337. Filtration of Feed-water , 628 

338. Deterioration or Wear and Tear of Boilers 629 

339. Overheating of Boilers 629 

340. Unequal Expansion and Contraction of Boilers 630 

341. Corrosion External 631 

342. " Internal 632 

343. Pitting, Wasting, and Grooving 634 

344. Repairs. General 635 

345. Patches 635 

CHAPTER XXVIII. 

BOILER INSPECTION AND TESTING. BOILER-EXPLOSIONS, 

346. Boiler-inspection 637 

347. The Steam-pressure Test 638 

348. The Hot-water-pressure Test 638 

349. The Cold-water-pressure Test or Hydrostatic Test 638 

350. The Hammer Test. 639 

351. Boiler-explosions. General 639 

352. Boiler Ruptures because too Weak 640 

353. " " from Excess of Pressure 641 

354. Theory of Boiler-explosions 642 

355. Energy resident in Hot Water under Pressure 642 

356. Reaction in Boiler-explosions 643 

357. Procedure when a Boiler is in Danger of Rupture 644 

PART III. 
CHAPTER XXIX. 

MANAGEMENT AND RUNNING OF ENGINES, 

358. General 645 

359. To Start a Non-condensing Engine 645 

360. " " " Condensing Engine ^..c 647 

361. " " *' Compound Engine 648 

362. Lubrication of the Engine 649 

363. " " " Cylinder and Valves , 649 

364. Graphite as a Lubricant. 652 

365. Lubrication of Bearings .' 652 

366. Tests of Lubricants 656 

367. Accidents in the Engine-room 657 

CHAPTER XXX. 

TESTING OF THE POWER PLANT FOR EFFICIENCY. 

368. General 660 

369. The Boiler- test 660 



XVin TABLE OF CONTENTS, 

t 

PAR. - PAGE; 

370. The Flue-gases , 66 r 

371. The Calorimeter 662 

372. Report of a Boiler-test 662 

373. The Engine-test 663 

374. The Dynamometer 663 

375. The Indicator 664 

376. Deductions from the Indicator-card 666 



CHAPTER XXXI. 

GENERAL REMARKS UPON THE POWER PLANT, 

377. Concentrated or Subdivided Steam-power 668 

3 78. Distribution of Power by Electricity, Gas, or Air 670 

379. Location of a Power Plant 671 

380. Construction of a Power House 673 

381. Arrangement of the Power Plant 674 

382. Fire-protection of the Power Plant 675 

383. Floors of the Power Plant 675 



LIST OF ILLUSTRATIONS. 



FIG. PACK 

1. Typical Horizontal Engine (C. and G. Cooper) 12 

2. Right-hand and Left-hand Engine v 14 

3. Throw Over and Under , 14 

4. Yoke Mechanism, Clayton Compressor 16 

5. Oscillating-cylinder Engine, Danube River ig 

6. Reciprocating Parts of Case Oscillating Engine 20 

7. Case Oscillating-cylinder Engine 20 

8. Root's Trunk-engine 21 

9. Bacon's Trunk-engine 22 

ID. Engine of H. M. S. Bellerophon 24 

11. Back-acting River-boat Engine, S. S. Belle 25 

12. Back-acting Engine of H. M. S. Agincourt 27 

13. Vertical Blowing engine, Back-acting 28 

14. Rand Horizontal Back-acting Air-compressor 29 

15. Vertical Steel-rod Frame, Hungarian State Railway 32 

16. Inverted Vertical Engine, Bethlehem Roll Mill 33 

17. Typical Fore-and-aft Triple-expansion Marine Engine , . 34 

18. Inverted Vertical Allis Pumping-engine at Milwaukee 35 

19. Vertical Pumping-engine with Overhead Fly-wheel 37 

20. Inclined Diagonal Engine of L. B. & S. C. Ry 38 

21. Inclined Engine 3g 

22. Inclined Engine for Pumping (Gaskill) 40 

24. Combined Horizontal and Vertical Engine 41 

30. Beam-engine of Skiddy 44 

31. Beam-engine, Cruiser Chicago 46 

32. Leavitt-Lawrence Beam-engine 47 

33. Gaskill Beam-engine with Horizontal Beam 48 

34. Dean Triangular-beam Pumping engine 49, 

35. Corliss Pawtucket Pumping-engine 50 

36. Gaskill Beam Pumping-engine gr 

37. Copeland's Side-lever Marine Engine of 1849 52 

38. Oscillating-beam Engine of U. S. Monitor Monadnock 53 

39. Silsby and La France Rotary Engine 55 

40. Baldwinsville Engine 56 

xix 



XX LIST OF ILLUSTRATIONS, 

FIG. PAGE 

41. Challenge Reversible Rotary Engine 57 

42. Bramah Engine 58 

43. Dow's Steam Turbine 62 

44. " " ** 62 

45. Parson's Steam Turbine. 63 

46. Delaval Steam Turbine 64 

47. Dake Square-piston Engine 64 

48. Walters Pendulum-engine 65 

49. West's or Coil's Disk-engine 66 

50. Gardner Three-cylinder Engine 67 

51. Hicks Engine , 68 

52. " " 68 

53. Wells' Balanced Engine 69 

^o. Cornish Pumping-engine of Brooklyn Water-works 73 

61. Cornish Cylinder Section 74 

62. Cornish Cataract Section 76 

63. Westinghouse Longitudinal Section 78 

64. " Transverse Section 79 

^5. Willans Single-acting Section. 80 

^6. Rectangular Indicator-diagram , 81 

67. Indicator-diagram with Expansion 82 

'68. Condensing and Non-condensing Engine Diagram 86 

69. Condenser of River-boat Engine of Francis Skiddy 92 

70. Surface Condenser of Marine Engine 93 

71. Wheeler's Surface Condenser 94 

72. Fittings for Condenser-tubes •; 96 

73. Cold- well Surrounds Jet Condenser and Air-pump 98 

74. Worthington Self-cooling Condenser , 100 

75. Blake Combined Air and Circulating Pump for U. S. S. Maine.. .... 103 

76. Ransom Gravity Condenser , 106 

77. Bulkley Siphon Condenser, General ....,.,, 107 

78. *' " " Section 108 

79. Worthington Ejector Condenser 109 

80. Ejector Condenser on Marine Engine iio 

81. Morton Ejector Condenser iii 

82. Schutte Ejector Condenser 112 

83. •' " •' Section 112 

84. " ** " General 113 

85. Pump-condenser (Craig and Brevoort) , 114 

^o. Indicator-diagram with Early Cut-off . , 116 

91. Compound Beam Pumping-engine for Philadelphia Water- works by 116 

F. E. Graff 120 

92. Ball Tandem Compound 121 

93. Watertown Tandem Compound 122 

94. Porter Steeple Compound 123 

95. Cross Compound Engine (Houston, Stanwood & Gamble) 123 

96. Inclined Compound 126 

97. Indicator-diagram, Compound Engine 128 



LIST OF ILLUSTRATIONS. XXI 

FIG. PAGE 

98. Combined Indicator-diagram 129 

99. Triple-engine Diagram 130 

105. Arrangement of Cylinders of Triple Engine (Thurston) 132 

106. " " " " Quadruple Engine (Thurston) 133 

107. High-pressure Receiver, Worthington Pumping-engine 135 

108. Tandem Compound Pumping-engine (Worthington) 136 

109. VVestinghouse Compound Engine 137 

1 10. Portable Engine (Hoadley) 145 

111. Throttling-engine Cards 147 

312. Cut-off-engine Cards 148 

113. Indicator-diagram with Loop , 151 

120. Three-way Plug-cock 155 

121. " " 155 

122. Four-way Plug-cock 155 

123. " " 155 

124. Plain Slide-valve 157 

125. Slide-valve in Central Position 157 

126. Eccentric is a Crank 160 

127. Trammel 162 

128. B Valve 163 

129. Valve with Lap 164 

130. Valve with Lap Ready to Open 165 

131. Valve with Lead , 168 

132. Valve-rod and Chest with Trammel 168 

133. Motion-curve with no Lap, not Lead 172 

134. Motion-curve with a Lap, not Lead , . . 173 

135. Motion-curve with a Lap and Lead 174 

136. Motion-curve with Increase of Valve-travel 175 

137. Motion-curve, Method of Drawing Mechanically (from Forney) 176 

138. Polar Diagram with no Lap 177 

139. Polar Diagram with Lap 177 

140. Polar Diagram with Lap and Lead 179 

141. Design of Valve and Seat 180 

142. Design of Diagram when Lap is to be Found 182 

143. Design of Diagram when Cut-off is to be One Half Stroke 183 

144. Meyer Riding Cut-off 185 

145. Two Valves in Two Chests 186 

146. Porter-Allen Cylinder 187 

147. Short-ported Valve-design , 190 

148. Buckeye Valve-gear , 191 

149. Allen Valve 192 

1 59. Pressure-plate and Valve of Atlas Engine 197 

160. Gridiron Slide-valve 193 

161. Multiported Valve-seat, Worthington Pump 193 

162. Double Piston-valve, Mead & Dick Engine 195 

163. Piston-valve (Armington & Sims) 196 

164. Fixed Pressure- plate, Richardson Balanced Locomotive Valve 198 

165. Pressure-plate Balance of Woodbury Engine 199 



LIST OF 



FIG. PAGE 

166. Porter's Pressure-plate 200 

167. Sweet's Pressure-plate 201 

168. Relief-ring for Valves 201 

169. Giddings Valve and Internal Steam 202 

1 70. Poppet-valve and Chest of Francis Skiddy 203. 

171. Outside Cam Valve-gear 204. 

1 72. Part of Western River-steamboat Valve-gear 205 

173. Part of River Valve-gear 205 

174. Cam of Varied Face 206- 

175. Winans Locomotive Cam 206- 

176. Porter Lever-cam 208 

1 77. Part of Western River Cam-gear 209* 

180. Trip-motion of Greene Valve-gear 211 

181. Plug-valve in Corliss Cylinder. 212 

182. Fishkill Landing Corliss Engine 213 

183. Payne Corliss Engine 217 

184. Bates Corliss Engine 218 

185. Steam-thrown Valve of Babcock & Wilcox Engine. .. ., 219' 

186. Gab-hooks 222: 

187. V Hook 223 

188. Stephenson Locomotive Link-motion from P. R. R 222 

189. Skeleton of Stephenson Link-motion 225 

190. Gooch Link-motion 227 

191. Joy Valve-gear, Marine. ... 229 

192. Joy Valve-gear Diagram 229 

193. Joy Valve-gear, Stationary 230 

194. Walschaert or Hensinger von Waldegg Valve-gear 231 

195 . Marshall Valve-gear 232 

196. Allen Link 237 

197. Meyer Valve-gear 237 

198. Watertown Trapezoidal Ports 234 

199. Rider Cut-off Valve , 238 

2CO. Sliding Valve-seat under Valve 239. 

205. Skeletons of Governor Mechanisms. .. 245 

206. Diagrams for Spindle-governors 246 

207. Twiss Engine with Loaded Porter Governor , . . , 248 

208. Steinlen Approximate Parabolic Governor 251 

209. Buss Governor 252 

210. Babcock & Wilcox Governor 252 

211. Pickering Governor 253 

212. Waters Governor 253. 

213. Gardner & Wright Spring-governors 254 

214. Armington & Sims Shaft-governor 255 

215. Mead & Dick Shaft-governor. 257-8 

216. McEwen Inertia Shaft-governor 259 

217. Parabolic and Crossed-arm Governor Diagram 25(> 

218. Resistance-governors 261 

219. Fuller Marine Governor 264 



LIST OF ILLUSTRATIONS, XXlU 

FIG. PACK 

225. Tank Bed-plate of Watertovvn Engine 267 

226. Corliss Bed-plate of Wetherill Engine. 26S 

227. Section of Bed-plate of Lane & Bodley Engine 269. 

228. Tangye or Buckeye Engine Bed-plate 27a 

229. Straight-line Engine Bed-plate 272 

230. Bates-Corliss Foundation for Tandem Engine. 277 

231. Foundation-template 279 

232. Shaft-bearing Adjustments (Lane & Bodley) 285 

233. Westinghouse Relief-valves, Ide Breaking Cap and Marine Relief-valve 291 

234. Joints for Steam-jackets 293 

235. Box-piston from Locomotive Practice 294 

236. Baldwin Locomotive Piston 295 

237. Plate-piston from Locomotive Practice 296 

238. Joints for Piston Packing-rings. . 29& 

239. Durfee's Piston of Wyandotte Engine 300' 

240. Steam-packing for Plate-pistons 301 

245. Jerome Metallic Packing for Rods 307 

246. Katzenstein's Metallic Packing for Rods 308 

247. Johns Metallic Packing for Rods 309 

260. One-guide or Bogie Locomotive Cross-head 312 

261. Slipper Cross-head and Guide, Straight-line Engine. . . .* 313 

262. Lane & Bodley Cross-head 315 

263. Ide Engine Cross-head 316 

264. Bates Engine Cross-head 316 

266. Woodbury Engine Cross-head 318 

270. Bates Engine Connecting-rod 322^ 

271. Closed Stub of Lane & Bodley Connecting-rod 324. 

272. Stub End of Woodbury Connecting-rod 325 

273. Stub End of Mattes Connecting-rod 326 

274. Hunt Ball Stub End 326 

280. Shaft, Overhanging, for Cross Compound 330- 

2S1. Shaft with Three-throw Crank 33C> 

282. Crank of Cast Iron 331 

283. Crank of Steel with Cast Counterbalance, Case Engine 332 

284. Crank Counterbalance Disk, Skinner Engine 333 

285. Crank-shaft Built up, S. S. Rome and Alaska 334. 

286. Thrust and Propeller Sections of Marine-engine Shaft 336 

287. Stern Bearing for Marine-engine Shaft 338 

288. Bates Engine Crank bearing and Bed-plate 339 

289. Eccentric and Strap 3Jo 

290. " " ** 341 

291. Fly-wheel Design (Busbridge) 347 

292. Fly-wheel Design, Leavitt's Boston Sewage Pumping-engine 347 

300. Slip and Corrugated Expansion-joint 354. 

301. Flange Expansion-joint 355 

302. Hartford Pipe-hanger 356 

303. Hartford Side Outlet from Pipe or Drum 357 



1 



XXIV LIST OF ILLUSTRATIONS. 

PIG. PAGE 

304. Albany Steam-trap , 358 

305. Centrifugal Separator and Water-pocket 359 

306. Receiver Separator. 360 

307. Mosher Separator. 361 

308. Westinghouse Steam-loop 361 

309. Spiral Riveted Pipe 364 

310. Various Exhaust-heads ,., 365 

311. Edminston Oil-filter 366 

312. Oil-separators 367 

313- " 367 

318. Curving Rolls , 382 

319. Curving Rolls, Acting of 383 

320. Curving Roll (Sellers) 383 

321. Erie City Boiler 384 

322. Flanging Press 386 

323. Flexure of Lap-joint 390 

324. Punch for Plate (Hilles & Jones) 391 

325. Punch and Die 392 

326. Punch (Kennedy's) 392 

327. Half-blind Hole 393 

329. Steam-riveier (Sellers) 396 

330. Hydraulic Riveter (Sellers) 397 

331. Forms of Rivets 400 

332. Lap-joint, Single Rivet 401 

333- " " " 402 

334. Lap-joint, Triple 402 

336. Flexure of Single Lap 403 

337. Lap-joint and One Cover. . . , 403 

338. Double Butt-joint 404 

339. Double-butt Rivet-joint (Leavitt) ., . . 405 

340. Failures of Rivet-joint 405 

341. Corrugated-flue Furnace with Combustion-chamber and Through- 405 

stay, U. S. S. Yorktown 409 

342. Stay-bars for Heads (Hartford) •• 409 

343. Stays for Heads (Hartford) 410 

344- " " '* " 411 

345. " " " " 411 

346. " " •• " 412 

347- " " " " 413 

348. Locomotive Fire-box Stays (Baldwin) 415 

349. Locomotive Fire-box Stays (Belpaire) 415 

350. Lukens Manhole 417 

351. Manhole Seating, Hartford 418 

352. " " " 419 

353. Scheme of Diagonal Brace, Hartford 414 

354. Edge-planing Machine (Hilles & Jones) 420 

355. Connery Concave Calking 420 



LIST OF ILLUSTRATIONS, XXV 

FIG. PAGE. 

360. Old Wagon-boiler, Watt's Type 423 

361. Plain Cylinder-boiler 424 

362. Plain Dome, Hartford » 426 

363. Reinforced Dome, Hartford 427 

364- '• " " 428 

365. Dome with Neck to Boiler 429- 

366. " " " " " 429 

367. Boiler with Transverse Drum or Pipe 430 

368. Boiler with Perforated Dry Pipe 431 

369. Dome with Stays 432 

370. Elephant or Union Boiler (Holley) 435 

371. French or Double Boiler 436 

372. Weimer Long Blast-furnace Elephant Boiler , , . . 436 

373. Circulation in Drum-boiler (Hartford) 437 

374. Bump-joint for Flues 439 

375. Rand Two-fiue Boiler 443 

376. T-iron Ring 441 

377. Angle-iron Ring., 442 

378. Adamson Loop-ring 442 

379. Six-inch Flue-boiler (H. S. & G.) 44a 

380. Serve-tube 446 

381. Lip or Tit Drills 446 

382. Tube-expanders 447 

383. Expanded Tube 448 

384. Steam-chimney for a Marine Boiler 478 

385. Wharton-Harrison Sectional Boiler 456 

386. Harrison Details 457 

387. Stirling Boiler. 458 

388. Cahall Boiler 459 

389. Babcock & Wilcox (Longitudinal Section) Boiler 461 

390. Root Boiler 462 

391. Heine Boiler 467 

392. Babcock & Wilcox Detail 465. 

393. " " " " 46s 

394. Root Detail 466 

395- " " 46s 

396. Detail of Zell Sectional Boiler 463, 

397. Allen IncUned-tube Boiler 468 

398. Silsbe Boiler 469 

399. Cornish Boiler 473 

400. Lancashire Boiler 474 

401. Strong Breeches Boiler 475 

402. Galloway Boiler 475 

403. Marine Three-furnace Boiler 476 

404. . " " " 477 

^ 405. Corrugated Flue 479 

406. Scotch Drum Marine Boiler with Two Furnaces 479 



XXV 1 LIS T OF ILL US TRA TIONS. 

FIG. PAGE 

407. Boiler of Ferry-boat Bergen 479 

408. Marine Boilers, Fire-tube , 480 

409. Marine Boilers, Water-tube 480 

410. Boiler of Ferry-boat Orange 481 

411. Wagon-top Structure for Locomotive Boiler 483 

412. Locomotive Boiler, Union Pacific Railway , 484 

413. HoUey Locomotive Boiler 485 

414. Wootton Fire-box Boiler 485 

415. " " " ..• 487 

416. Monarch Boiler 488 

417. Economic Boiler, Side Section 490 

418. Upright Boiler , 491 

419. Manning Upright Boiler 491 

420. Upright Boiler with Submerged Tubes 493 

421. Corliss Boiler 494 

422. Reynolds Arrangement of Tubes 495 

423. Fire-engine Boiler 496 

.424. '* " 497 

425. Almy Boiler 499 

426. " " 500 

427. Thornycroft Boiler 501 

428. Ward's Boiler 501 

429. Herreshoff Boiler 502 

430. Locomotive Fire-box with Fire-brick Arch 486 

431. Holley Boiler-setting, showing Mud-drum 438 

432. Louisville & Nashville Locomotive-boiler 489 

433. Beach Water-leg, Front 516 

436. Newark Hewes & Phillips Setting 506 

437. " " " " 507 

438. Hanging by Eyes , 509 

439. Long Boiler cut in Two (Durfee) 510 

440. Rand 512 

441. " Boiler-front 514 

442. Rand Setting 515 

443. Houston, Stanwood & Gamble Half-front 517 

444. Hartford Setting 519 

445. Baldwin 522 

446. " Setting 523 

447. Typical Grate-bar 524 

448. ^tna Grate 525 

449. Dumping-grate 526 

450. Step-grate 528 

451. Coxe Travelling-grate 530 

452. Babcock & Wilcox Stoker 531 

453. Wilkinson Stoker 532 

454. Roney Stoker 533 

455. American Stoker 534 



LIS T OF ILL US TRA TIONS. XXVI 1 

TIG. PAGE 

456. Side View Hartford Setting 535 

457. Side View Sterling Setting 536 

4=8. End View Sterling Setting , .... 538 

459. Fishkill Landing Extended Front 539 

460. Hartford Plan-view of Setting 540 

461. Stanwood Half-front 541 

462. Jarvis Furnace 542 

463. Pittsburgh Two-flue Boiler 544 

464. Uptake Flues of Sheet Iron 547 

465. Damper-regulator 549 

466. " 550 

467. Chimney-stack 552 

468. *' o 552 

469. Externally-fired Galloway Boiler 572 

470. Hawley Down-draft Furnace 575 

471. Marden Down-draft Furnace 576 

472. Diaphragm-gauge 579 

473. Bourdon Gauge 580 

474. Crosby Gauge 580 

475. Gauge-siphon 581 

476. Gauge-glass and Boiler-front 584 

477. Column-pipe 584 

478. Safety Gauge-glass , 585 

479. English Gauge-glass 586 

480. Weighted Gauge-cock, Fairbanks' Duplex 588 

481. Mississippi, American and Regester Gauge-cock 588 

482. Fusible Plug 590 

483. Feed-pipe partly closed with Scale 592 

484. Check-valves 594 

485. " •• 594 

486. Blake Pump 597 

487. Injector Principle (Forney) 599 

488. Injector, Sellers, of 1876 , 601 

489. Injector, Schutte 601 

490. Hoppe's Feed-water Heater. 603 

491. Tubular Feed-water Heaters 604 

492. " " " 606-7 

493. Economizer, Greene's Type 608 

494. Safety-valve, Lever Type 613 

495. Pop Safety-valve * 614 

496. Brush and Scrapers for Tubes 619 

497. Jet Cleaner 620 

498. Babcock & Wilcox 627 

499. Victor Filler 628 

500. Grooved Plate » 63 1 

501. Grooved Plate 631 

502. Cylinder and i cubic foot of water 643 



XXVIU LIST OF ILLUSTRATIONS, 

FIG. PAGE- 

503. Cylinder Oil-pump 650 

504. Pipe-lubricators 651 

505. Sight-feed Oil-cup 653 

506. Crank-pin Lubricator 654 

507. Webbing-surface for Lubricator. , 654 

508. Grease-cups 655 

509. Zeuner's Deduction of Formula 683 

510. " " " " 685 

511. Deduction of Bursting- pressure of Cylinders 689 

512. " '* " " " " 689. 



THE MECHANICAL ENGINEERING 

OF 

POWER PLANTS. 



CHAPTER I. 
INTRODUCTORY. 

I. Sources of Motor Energy.— There are three great 
sources of force for industrial uses. The first to be applied is 
the muscular force of men and animals. The second is the 
force called the force of gravity by which the earth attracts all 
masses towards its centre. The third is the group of forces 
which are due to chemical combinations; the two most im- 
portant of these are the forces of heat and electricity. 

It is obvious that these latter or the chemical forces are by 
far the most important. The reasons for this are, first that 
the muscular force in men or animals is naturally limited by 
the capacity of the units and by their endurance. There is 
furthermore no considerable reserve store of energy in each 
unit to be drawn on if more is required. The force of gravity 
becomes available as a motor force when a weight or mass is 
lifted to a higher level and is permitted to descend to a lower 
one. Solid weights are only of service when lifted by some 
other mechanical force; the only weights which are otherwise 
lifted to high levels independent of man are air and water. 
The latter is lifted by the sun in evaporation to high levels of 



2 MECHANICAL ENGINEERING OF POWER PLANTS. 

land, and the winds are produced when colder and heavier air 
descends and displaces the lighter warmed air. It would 
appear from this that all water-motors and windmills are really 
heat-motors in the last reduction. Gravity, therefore, as a 
motor force is dependent upon the availability of higher levels 
at which a mass of water can be accumulated, and an adequate 
reservoir in any particular region or an adequate flow from a 
source is a necessary condition for the use of water-motors; 
and while there is an abundance of energy present in the 
atmospheric ocean at the bottom of which all industry is carried 
on, the reliability, controllability, and capacity which must 
belong to the satisfactory working of a motor are lacking to 
windmills in most places where continuous service is required. 

The energy resident in coal or other fuel and to be liber- 
ated as heat upon combustion is not subject to this class of 
limitations. An enormous capacity for doing work is stored 
in a very compact bulk: it is liberated from the fuel gradually 
as required, and yet the limits of available quantity have never 
been reached. It is to be had in very nearly all regions, and 
where it is not native it can be easily transported. If desired, 
the energy resident in it can be transported in the form of 
gas from a native spot through pipes to the place where it is 
required. As the engine is to be treated as a device for ren- 
dering available the potential energy present in fuels, and 
which when liberated from the fuel appears so conveniently in 
the form of an elastic tension of steam-gas, it becomes at once 
apparent why the steam-engine has received the development 
and distribution which has made it a primary factor of modern 
civilization. 

While every one considers that the near future is to reveal 
a method for generating or liberating energy directly from 
fuel in the form of electromotive force, and this is now done 
by the chemical actions in various electric batteries, the im- 
portance and extent of this development at this writing re- 
move it from the category of the large-scale installations such 
as are at present under consideration, and for many uses 
present methods are likely to prevail even in such future. 



IN TROD UCTOR V. 3 

2. Analysis of Development in a Power Plant. — In the 

power plant which is to be considered as a typical example 
the steps or succession of events may be considered to be five. 
First there is the generation or liberation of the stored or 
accumulated energy. In a steam-power plant this process 
occurs in the furnace or fire-box of the boiler. Second, the 
storage or accumulation of the energy of heat thus liberated 
from the fuel in a suitable vessel or reservoir from which it 
may be drawn off as required. This is the boiler. Third, the 
appliance whereby the energy stored in the boiler as potential 
energy is transformed into actual energy by being made to 
exert force through a prescribed path under the control of 
capable intelligence. This is the engine. Fourth, the con- 
trolled force acting through the controlled space or path is to 
be transmitted from the engine or prime mover to the machine 
or apparatus which is to be driven. This gives rise to 
mechanism and transmissive machinery. Fifth, the industrial 
work of manufacturing, propelling, or whatever may be the 
function of the generated power, is the last link in the chain. 

It is obvious that the last link in the chain is as extensive 
as the entire field of industry; and the transmission of power 
is itself a subject of sufficient importance in its various fields 
of electrical transmission, compressed air, high-pressure 
water, shafting, belting, gearing, or linkage to make a depart- 
ment to be treated by itself. The steps of generation or 
liberation, the storage and the release and transformation of 
energy from the fuels which form the first three departments, 
are to form the subject of this treatise. 

It will at once suggest itself that while these successive 
steps are present in all power plants, in some it may happen 
that more than one is taken at once. In water-power plants, 
the liberation or storage of energy is done for the engineer 
before his work begins. This is also true for the windwill 
motor. In the gas or hot-air or direct-combustion engine 
there is no storage step in the process, but the energy must 
be utilized as fast as it is released. On the other hand, fon 
the gas-engine plant which produces its own f^as there ig ^ 



4 MECHANICAL ENGINEERING OF POWER PLANTS, 

step of accumulation of energy which is lacking when solid 
fuel is burned directly under the boiler. 

3. The Units of Output of a Power Plant. — The product 
of a force expressed in units of weight or pressure acting 
through a space expressed in units of length gives the work 
done by a motor. If the units are pounds and feet, the 
work will be expressed in foot-pounds. If the units are the 
kilogram and the meter, the work is expressed in kiio- 
grammeters. The foot-pound or the kilogrammeter being too 
small for convenient use, the term horse-power was early 
found useful to denote the capacity or delivery of work by 
motors. It was introduced by James Watt as early as 1775. 
The English or American horse-power is 33,000 foot-pounds 
exerted in. one minute. The metric horse-power is 75 kilo- 
,grammeters per second or 4500 per minute. The following 
table shows the relations of certain of these units of work to 
each other: 

English. French. Austrian. 

Horse-power. Foot-pounds Kilogrammeter Foot-pounds 

per Minute. per Minute. per Minute. 

English and American. 33,000 4,562.46 25,23-3.6 

French 32,548.2 4,500 25,420.8 

Austrian 33,034.2 4,567.14 25,800 

The English H. P. is i. 01 385 force de cheval. 

The French force de cheval is 0.986337 English H. P. 

The steam-engine being a heat-engine, it becomes easy 
to pass from the energy resident in a unit of heat to the 
horse-power. The historic experiments of Joule and the 
later determinations by Rowland and other physicists show 
that the work of a force in foot-pounds can be transformed 
into heat-units directly, in the relation that , according to Joule, 
772 foot-pounds or, according to Rowland, 778 foot-pounds 
are the dynamic equivalent of one unit of heat. In metric 
units and the centigrade scale this corresponds to 428 kilo- 
grammeters per degree centigrade. In electrical plants the 
unit of work is called the joule, which is practically equiva- 



IN TR OD UCTOR V. 5 

lent to the energy expended per second by the international 
ampere against an international ohm, and the unit of power 
is the watt, which is practically equivalent to the work done 
at the rate of one joule per second. The watt is ^J-g- of the 
energy in one horse-power, from which it results that one 
kilowatt is equivalent to 1.34 horse-power. 

4. Measurement of Output. — Quantity of work in foot- 
pounds or other units delivered by a motor can be measured 
•either by the work supplied to it or by the work delivered 
from it. The work delivered from it is often called the net 
or effective horse-power. As it is often measured experimen- 
tally by means of a dynamometer or brake whereby power is 
transmitted or absorbed, it is termed brake horse-power or 
dynamometer horse-power, which have the same meaning for 
these reasons. 

The energy delivered to the steam-engine is usually meas- 
ured by an instrument first devised by James Watt which is 
called the Indicator. The indicator is an apparatus whereby 
the pressure exerted on the piston of the steam-engine is 
measured or recorded at each point of the travel of such piston, 
and the mean pressure of the steam in the cylinder multiplied 
by the space through which it acts gives the energy supplied. 
This is usually called the indicated horse-power. 

Nominal horse-power is an old term now properly dis- 
used, which was based on an untenable assumption that all 
engines of a given diameter of cylinder were of the same 
horse-power, whatever the pressures or speeds used. 

5. The Scheme of Classification. — Inasmuch as the power 
plant is always designed by the engineer for the doing of a 
specified kind of work, the whole design of the plant for the 
liberation or storage of energy will be based upon the magni- 
tude of that useful resistance to be overcome. For this reason 
and because there are advantages attaching to the study of 
the boiler after the student has become familiar with the 
engine, this latter course has been pursued in the arrange- 
ment of the chapters. The engine will first be studied; then 
the boiler and furnace; and the combined plant of eng-ine and 



O MECHANICAL ENGINEERING OF POWER PLANTS, 

boiler taken together will be studied last. The following 
system of classification will therefore be adopted 

1. The Engine. 

a. By Mechanism. 

b. By Speed and Proportions of Cylinder. 

c. By Use of Steam. 

d. By Method of Control. 

e. Construction and Assembling of Engines. 
/. Piping and Steam Appliances. 

2. The Boiler. 

a. Types. 

b. Construction of a Typical Form, 
r. Setting and Accessories. 

d. Wear, Tear, Deterioration, and Repairs. 

e. Testing for Strength ; Explosions. 

3. Plant, Engine, and Boiler. 

a. Care and Management. 

b. Testing for Efficiency, 

c. Location and Arrangement of Plant. 



CHAPTER II. 
THE MECHANISM OF ENGINES. 

6. The Horse-power of a Cylinder. — It has been found 
most convenient to transfer the potential energy of steam- 
gas under pressure into actual energy in foot-pounds by caus- 
ing the pressure of the steam to move a disk or piston back 
and forth in a cylinder in which it fits tightly enough to pre- 
vent escape of the steam. The cylinder is usually circular in 
cross-section. It is obvious that if the pressure of the steam- 
gas be denoted by the letter P in pounds per square inch of 
area, and the area of the piston be denoted by the letter A^ 
the total pressure of pounds which moves that piston in this 
* cylinder will be represented by the product PA. 

The traverse or movement of the piston in a cylinder 
cannot be continuous in one direction unless the cylinder be 
of infinite length. The motion of the resistance will usually 
be continuous in the same direction, while the motion of the 
piston receiving the effort must be an alternating back-and- 
forth motion — called a reciprocating motion — and a proper 
mechanism must connect the two ends and transform the 
motion of the piston into the continuous motion required for 
the resistance. This necessity compels the design of those 
mechanisms of engine which experience has shown to be the 
most usual and convenient. 

If the traverse or movement of the piston be represented 
by the letter L expressed in feet, and the letter N denote the 
number of times per minute which the piston traverses the 
length Z, the product LN will represent the number of feet 
per minute through which the total force denoted by PA has 

7 



8 MECHANICAL ENGINEERING OF POWER PLANTS. 

been moved. The work per minute done by such a cylinder 
will therefore be expressed by the equation of the form 

W = PALN 

in the compound unit foot-pounds. Since there are 33,000 
foot-pounds in one horse-power, if both members of this equa- 
tion be divided by 33,000 the equation appears in the form 

H.P. = ^^^. 

33,000 

It is to be noted that, while A is in inches and L is in feet, 
this causes no confusion in the multiplication. The numer- 
ator of the fraction is often written PLAN, as being more 
easily remembered. 

. Since A is the area of the base of the cylinder inside and 
L is its altitude, then LA is the volume of the cylinder. 
That volume is filled N times per minute; whence it follows 
that PLAN may be written PV, in which V denotes the 
volume of steam-gas furnished to the engine-cylinder if the 
pressure P is uniform and constant at all instants of the 
minute. If P varies from the constant pressure prevailing 
in the boiler or reservoir of pressure, as it usually does, the 
value for P must be the value for the mean pressure, ascer- 
tained by calculation or by experiment. 

7. Horse-power of the Resistance. — The useful resist- 
ance or the work to be done by an engine is also given or 
measured by the foot-pound unit. If the useful resistance is 
the lifting of weights, as in hoisting or in pumping, or if it is 
the moving of masses without lifting, as in propulsion in water 
or on level land, the determination of the foot-pounds is 
obvious. But in the cases where the continuous motion, (as 
is usual in factory practice and in much of power-plant prac- 
tice), is taken from the circumference of a revolving wheel 
or drum, the foot-pounds are found directly by multiplying 
the speed in feet per minute at the circumference of such a 
wheel by the effort or pull expressed in pounds which is 
exerted at such circumference. 



THE MECHANISM OF ENGINES. 9 

8. Transformation of the Horse-power Formula, — It 

will be apparent that the horse-power of a cylinder motor will 
increase with the pressure, with the diameter of the cylinder, 
with the length of the cylinder, and with the number of re- 
ciprocations of the piston. 

In an engine once constructed A and L are fixed or 
constant, and the factor 33,000 is constant. If then the 

AL 

initial AT denote the fraction , the horse-power formula 

33,000 ^ 

may be written 

H.P. = PNK, 

in which K may be called the engine-constant. 

It will be further apparent, so far as the engine itself is 
concerned, that P and N can be increased, and with them the 
horse-power, without adding to the weight or bulk of the 
engine. 

It is not necessary that the path traversed by the piston 
should be a straight line. It can move in any closed curve, 
the most frequent of such curves being the circle. This 
difference gives rise to the first great division of the steam- 
engine into classes. Where the piston travels back and forth 
in a cylinder with a straight axis the engine will be called a 
reciprocating steam-engine. This is by far the most usual 
type, for reasons which will appear.* When the piston or area 
receiving the steam-pressure travels in a circular path con- 
tinuously in the same direction the engine is called a rotary 
steani-engine. The advantages and disadvantages of the rotary 
will be discussed hereafter. 

9. Essential Parts of a Reciprocating Steam-engine. — 
The condition referred to before (par. 6) for the transforma- 
tion of the alternating or reciprocating translation of the piston 
into the continuous rotation of the engine-shaft in one direc- 
tion has compelled the adoption of a mechanism or linkage for 
this purpose. To produce the rotation of the engine-shaft, 
the crank and connecting-rod is the almost universal device. 
The length of the traverse of the piston in the cylinder will 



lO MECHANICAL ENGINEERING OF POWER PLANTS. 

be twice the effective length of the crank: the length of the 
interior bore of the cylinder will therefore be twice the length 
of the crank, to which must be added the depth or length of 
the piston-disk in the direction of its motion, and the allow- 
ance for clearance at each end so that the piston shall not 
strike either head of the cylinder, and which shall permit the 
steam-pressure to get behind the piston when the latter is at 
the extremes of its motion. 

The motion of the piston in the cylinder must be trans- 
mitted outside to the mechanism which is to transform the 
reciprocating to rotary motion in the open air. This is done 
by the piston-rod, whose length must be sufficient to permit 
the piston to return to the end furthest from the hole through 
which the rod protrudes without drawing the rod inside. 
The rod further must slide in and out of the cylinder-head 
without permitting leakage of steam or condensed water. 
The device designed for this purpose is called a stuffing-box,, 
and the space for this stuffing-box adds something to the 
length of the rod. 

The end of the piston-rod is connected to the pin of the 
crank by what is called the connecting-rod. In the locomo- 
tive it is sometimes called the main rod or driving-rod. The 
term pitman is properly restricted to the connecting-rod 
which couples the crank-pin to a vibrating beam ; connecting- 
rod, however, is a general name. Its function is to provide 
for those components of the motion of the crank-pin for which 
the linear motion of the piston or its rod cannot provide, and 
for this reason it usually has a length from two and one-half 
to four times the length of the crank. When the crank has 
made a partial revolution it will be obvious that the thrust or 
pull of the connecting-rod transmitting the energy of the 
steam to the crank-pin will cause a cross-strain or bending 
effect upon the end of the piston-rod to which it is attached. 
This bending effect must be counteracted, since otherwise the 
hole for the piston-rod would wear out of round, whence 
leakage and other difficulties would ensue. Therefore the end 
of the piston-rod must be so guided that this shall be pre- 



THE MECHANISM OF ENGINES. 1 1 

vented. This is done by fitting to the outer end of the piston- 
rod a block or head which is called the cross-head in America, 
and the motion-block in England. It is arranged so as to be 
guided by plane surfaces or bars which are called the guides. 
These should be carefully adjusted to lie in a plane or planes 
parallel to the axis of the cylinder. 

The connecting-rod taking hold of the crank-pin causes 
the engine-shaft to revolve continuously in one direction in its 
bearings. It is usual to have the centre of these bearings in 
the same plane as the axis of the cylinder, although this is 
not an essential condition. On the engine-shaft will be the 
fly-wheel for regulating any variation of effort upon the crank- 
pin, and from this engine-shaft the power will be taken off, 
either by directly coupling the resistance to the shaft, as in 
steam dynamos, marine engines, rolling-mills and the like, 
or by belting or gearing from a wheel on the shaft or from the 
fly-wheel itself, as in usual factory practice. The valve- 
motion is usually driven from the shaft. 

10. General Features of a Typical Mechanism. — While 
different types of engines are marked by differences in detail. 
Fig. I herewith will represent the appearance of a typical 
horizontal steam-engine. It will be observed that the essen- 
tial organs of the mechanism enumerated in par. 9 are sup- 
ported by a massive casting. This casting is called the engine- 
bed or bed-plate, and serves not only to keep the various organs 
of the engine in fixed relation to each other, and to prevent 
undesired motion, but also serves as a means of securing the 
moving parts to a suitable foundation so as to secure stability. 
The bed-plate represents the fixed link in a kinematic chain. 
In the locomotive engine the bed-plate function is discharged 
by the frame of the engine to which the hauling appliances of 
the draw-bar are fastened in order that the frame of the engine 
may haul the attached train. In marine practice the bed- 
plate of the engine is securely fastened to extra heavy frames 
of the hull, so that the propelling effort exerted by the screw 
and transmitted to these frames may push the vessel forward. 

There are certain terms relating to the mechanism in 



12 MECHANICAL ENGINEERING OF POWER PLANTS. 




t 



THE MECHANISM OF ENGINES. 13 

general to which attention should be called at this point. It 
will be noticed first that when the crank-pin lies in the line 
drawn through the axis of the cylinder, the pressure of the 
steam upon the piston produces no effect to cause rota- 
tion of the crank. When the crank is in this position the 
engine is said to be on its dead-centre, or simply on its centre. 
Most engines have also another centre, usually coincident with 
this or nearly so, when the openings admitting steam to the 
cylinder are closed at both ends of such cylinder by their 
respective valve or valves. Provision must be made in large 
engines to turn the shaft past such dead-centre if by mis- 
management or accident it should become stopped there. 
Vertical engines are particularly liable to stop on the centre, 
and with the crank below the shaft. When the crank on the 
centre points towards the cylinder it is said to be on its inner 
centre. At i8o° from this, or when the crank points away 
from the cylinder, it is said to be on its outer dead-centre. 

The end of the cylinder which is towards the crank or 
shaft is usually called the crank end of the cylinder, and the 
end away from the crank is called the head end. It is some- 
times convenient to have the power from the engine taken off 
from one or the other side of the vertical plane through the 
axis of the cylinder; this gives rise to such an arrangement 
of the mechanism upon the bed-plate as to cause engines 
to be known as right-hand or left-hand engines. A right- 
hand engine is one in which the shaft of the engine which 
carries the fly-wheel and driving mechanism is at the right 
hand of the observer as he stands at the head end of the 
cylinder (Fig. 2). While it is usual to have one end of the 
engine-shaft supported upon the bed-plate, and the other end 
upon a separate bearing which is usually called the outboard 
bearing (a term borrowed from the practice prevalent when 
paddle-wheels were universal in marine engines and the bear- 
ing of the shaft was supported by an exterior guard over- 
hanging the water), yet very many designs, particularly for 
engines to be directly coupled to their resistance, have the 
engine-shaft driven by a double crank, whereby it is sup- 



14 MECHANICAL ENGINEERING OF POWER PLANTS, 

Fig. 2. 



@A^- 



RIGHT HAND ENGINE 



_..«il=^ 






"-Ti 



UFT HAND EHGINE 



-eSs- 



f 



BELT BACK 





Fig. 3. 



THE MECHANISM OF ENGINES. 15 

ported by a bearing on each side of the bed-plate. Such 
engines are called centre-crank engines. The typical marine 
engines are of this construction. Fig. i will be called a side- 
crank engine. 

An engine is said to throw over or under when the crank 
starting from its inner dead-centre rises above the axis line or 
descends below it upon the beginning of the stroke (Fig. 3). 
It is considered desirable to have an engine throw over 
when possible because the pressure due to the oblique direc- 
tion of the connecting-rod is always downward both upon the 
pushing and the pulling stroke. This is of advantage, first 
because the pressure upon the guides is resisted by the bed- 
plate in the direction of its greatest stiffness, and secondly 
because the lubrication of the upper surface of the lower guide 
is more convenient than the lubrication of the under surface 
of the upper guide, which has the pressure when the engine 
throws under. In the locomotive where the cylinders are in 
front of the driving-wheels, the engine must always throw 
under in going forward. 

The pressure on the guides due to the angularity of the 
connecting-rod diminishes as that connecting-rod becomes 
long in relation to the length of the crank. It has sometimes 
been urged against the connecting-rod as a device for trans- 
forming reciprocating into rotary motion, that it is wasteful 
and causes avoidable loss from friction. It can be proved that 
there is little in this argument, since an equality of work in 
the cylinder and at the crank will be secured by a less effort 
in pounds exerted at the latter point when the path of the 
latter is greater than that of the former. The condition of 
true harmonic motion for the piston is only secured when the 
connecting-rod is of infinite length. An equivalent for this 
condition is secured by using a yoke in the piston-rod whereby 
the pressure of the steam is always exerted upon the crank-pin 
in the direction parallel to the axis of the cylinder. This 
mechanism, shown in Fig. 4, has excessive friction near the 
dead-points, and is therefore used only where the rotating shaft 
has a regulating function merely and is intended to store up 



1 6 MECHANICAL ENGINEERING OF POWER PLANTS, 

energy for passing the centres while the main effort of the 
steam is transmitted through a continuous piston-rod, as in 
pumping, air-compressors and the Hke. 

It will appear hereafter that one of the functions of the 
rotary fly-wheel is to carry the engine mechanism past the 
kinematic dead-centres and the dead-centres of the valve- 
motion. If there is no fly-wheel to compel this result it must 
be secured by special arrangements, such as are features ia 
duplex and other direct-acting steam-pumps. 

The existence of a patent upon the crank and connecting- 
rod mechanism at the time of James Watt's first improvements 




Fig. 4 



in the steam-engine compelled him to the device which will be 
found in the very early examples of English engines whereby 
for one double stroke of the piston the engine-shaft made two 
or three revolutions. This result was obtained by attaching a 
gear-wheel to the connecting-rod which engaged with another 
upon the revolving shaft. As the fixed gear on the connect- 
ing-rod travelled around the gear on the shaft, the aggregate 
path of the latter was more than one revolution for one traverse 
of the piston. This gear was called the sun and planet motion^ 



THE MECHANISM OF ENGINES. 1 7 

but was discarded as soon as the right to use the crank 
became public property. 

The typical engine shown in Fig. i has but a single piston 
traversing a single cylinder. It is thoroughly practical to use 
more than one cylinder, in which case it is desirable that the 
two cranks of the mechanism of the separate cylinders should 
make an angle with each other whereby the inequalities of the 
effort upon the shaft occurring with one cylinder shall be 
compensated by putting the cranks in such relation that one 
shall be at its position of best advantage when the other is 
working with least effect. In two-cylinder engines this is 
secured by putting the cranks a quadrant apart, or quartering.. 
This is universal in locomotive-engine practice. When there 
are three cylinders, they will be put at 120° with each other.. 

11. Length of the Typical Reciprocating Engine.- — If 
the typical engine represented in Fig. I be supposed to have 
the connecting-rod of three times the length of the crank and 
be supposed to be turned so that the crank stands upon its 
outer dead-centre, it will appear that the length between the 
head end and the crank-pin of such engine is made of the 
following units: 

1. Cylinder, two cranks. 

2. Piston-rod, two cranks. 

3. Connecting-rod, three cranks. 

4. Allowances for stuffing-box, cylinder-heads, metal 

in piston, cross-head, etc. 
Total. Something over seven cranks in length. 
The exigencies which are imposed by the contracted space 
in vessels where the location and direction of the engine- 
shafts are fixed by the propelling mechanism outside of the 
hull have compelled the designers of engines for this condi- 
tion to modify the typical mechanism to suit their particular 
need. These designs have but a limited application on land^ 
where these conditions of restricted room are not felt. 

12. The Oscillating Engine. — If the connecting-rod of the 
typical mechanism be suppressed, the length of the engine 
becomes only four cranks and allowances. The motion of the 



1 8 MiLCHANICAL ENGINEERING OF POWER PLANTS. 

crank in the direction of the sines of the crank-angles requires 
to be provided for while the piston-rod slides in and out in the 
straight line through the stuffing-box. This compels the axis 
of the cylinder to change its direction continually in order 
that the piston-rod may always point towards the crank-pin, 
and therefore the cylinder must be so mounted upon suitable 
trunnions or pivots as to adjust itself accordingly. These 
trunnions should be constructed upon the axis through the 
centre of gravity of the cylinder, but in small engines they 
may be a part of the head end. The steam from the boiler 
usually enters the cylinder through the trunnion on one side 
and leaves it as exhaust steam through the other (Fig. 5). It 
is quite possible, however, to have both admission and 
exhaust functions in one trunnion. 

This design has received its widest application for the 
driving of paddle-wheels of side-wheel steamers, where it is 
desirable to economize room and to bring the weight of the 
cylinder as low down as possible. The height of the shaft 
above the water is fixed by the diameter of the wheel, and 
the slow speed of rotation compels a long stroke if the pistoriS 
are to travel a considerable number of feet per minute. The 
objections to this mechanism are, first, the power required to 
start and accelerate and to stop so great a mass as the 
cylinder of a large engine twice in a revolution ; second, the 
friction entailed by the motion of such heavy parts which do 
not move in the typical engine; third, the tendency of the 
trunnions to wear out of round and cause the steam connec- 
tions to leak; fourth, the tendency of the stuffing-box 
through which the rod protrudes and upon which the cross- 
strain is continuously acting to wear out of round and to leak. 

They make, however, a compact and somewhat cheap 
engine in their smallest sizes. They have been used in 
such sizes to enable the designer to secure very light weight 
^n the reciprocating mechanism, so that very high rotative 
speed is permissible without very high steam-pressure. Fig. 
6 shows how little mass can be demanded in such a design. 
A skeleton diagram, Fig. 7, shows also the use of a very long 



II 



THE MECHANISM OF ENGINES. 



19 




20 MECHANICAL ENGINEERING OF POWER PLANTS. 



stuffing-box connection to give leverage to the oscillating; 
cylinder 




Fig. 6. 




Fig. 7 

13. The Trunk-engine. — If the piston-rod of a typical 
engine with the cross-head at its end be reduced to a pointy 



THE MECHANISM OE ENGINES. 



21 



while the connecting-rod is retained, the engine is shortened 
by the length of two cranks and the stuffing-box allowances, 
and the pin upon which the connecting-rod has its vibratory 
motion becomes attached directly to the piston-disk. The 




Fig. 8 

vibration of the connecting-rod from its connection with the 
crank-pin must be permitted through the crank end of the 
cylinder, and at the same time this orifice must be so con- 
structed that it can be kept steam-tight. This difficulty has 
been solved by attaching to the piston a hollow cylinder or 



22 MECHANICAL ENGINEERING OF POWER PLANTS. 

trunk whose diameter is sufficient to permit the angular motion 
of the connecting-rod to take place within it, while its exterior 
finished surface slides steam-tight through the usual stuffing- 
box construction. The trunk is thus like a hollow piston-rod 
except that the cross-head attachments are at its piston end, 
and it is under no pull and thrusting strain, but is simply a 
device to insure steam-tightness. Fig. 8 i-llustrates an engine 
of this type in cross-section, with the added peculiarity that 




Fig. 9. 

the attachment of the connecting-rod is behind the real piston 
(67) whereby more oblique action of the connecting-rod is 
secured. In this design the hollow trunk is carried through the 
head end of the cylinder, which has the effect of making the 
annular area of the piston the same above and below. Quite 
frequently the trunk behind or beyond the piston is left out, 
so that one stroke is more powerful than the other by reason 



THE MECHANISM OF ENGINES. 23 

of the full area which receives pressure on one side and the 
annular area on the other. Such engines are often called half- 
trunk engines, and have been a favorite design for compact 
hoisting-engines (Fig. 9). These trunk-engines have been 
much used in marine practice for monitors and similar condi- 
tions where an engine was required to lie athwart ship and 
have but little vertical height (Fig. 10). The objection to 
them is the large diameter of the cylinder proper for any con- 
siderable power by reason of the loss of effective area entailed 
by the hollow trunk. It is usually more convenient to make 
the trunk cylindrical, but this is not necessary except for ease 
in packing the joint at the stufifing-box. The minimum sec- 
tion for the trunk would be an oval or rectangle with rounded 
ends (Fig. 9). As in the case of the oscillating engine, the 
trunk-engine is a cheap construction in its smaller sizes, and 
lends itself particularly well to designs where the pressure of 
the steam is to come on one side of the piston only, in what 
are called single-acting engines (see Fig. 64). The trunk 
serves also as a guide to the piston to prevent it from cocking 
or jamming from the oblique thrust of the connecting-rod 
when it has no guiding piston-rod. 

14. Back-acting Engine. — In the typical mechanism of 
the steam-engine the connecting-rod and the cross-head with 
its guides come between the cylinder and the crank so that 
the piston-rod and connecting-rod are together in tension or 
in compression, according as the effort of the steam is pulling 
or pushing upon the crank-pin. It is easily possible to bend 
the connecting-rod backwards from the cross-head, so as to 
extend behind the end of the cylinder, which has hitherto 
be&n called the head end, and to locate the crank and engine- 
shaft thus behind the cylinder as it were. It is usually neces- 
sary where the shaft is behind the cylinder to make use of two 
connecting-rods from the cross-head to the crank-shaft, to 
prevent cross-bending strain upon the cross-head, since the 
cylinder itself is in the line of the axis of the effort. These 
two connecting-rods may go to independent crank-pins, or the 
two connecting-rods may join behind the cylinder to form 
one, which in the axis of the cylinder at the back will trans- 



24 MECHANICAL ENGINEERING OF POWER PLANTS. 




I 



THE MECHANISM OF ENGINES. 



25 



mit the effort to a single pin. This type of design is by no 
means unusual for pumps, air-compressors, and blowing- 




Bradleij ^ Poates, Engr%N.Ti. 



Fig. II. 



engines, but has ceased to be in as general use for other pur- 
poses as in the beginning of steam-navigation. Fig. 1 1 



26 MECHANICAL ENGINEERING OF POWER PLANTS. 

shows this mechanism as it is appHed to a paddle-wheel 
steamer still in use for towing upon the Hudson River. 

The more usual form in modern vessels of war is to have 
the crank-shaft in the axis of the horizontal cylinder and quite 
close to its crank end. Two piston-rods protrude through the 
crank end of the cylinder, separated from each other by such 
a distance that one passes on one side and the other upon the 
other side of the shaft, and are joined together to a common 
cross-head beyond the shaft and at a sufficient distance from 
it to allow the connecting-rod from that cross-head to lap back 
between the piston-rods and take hold upon the crank-pin in 
the plane between them and all in the axis of the cylinder or 
symmetrical to it. This may also be done by three or four 
piston-rods instead of two. Fig. 12 shows an engine of this 
latter sort. The typical length is obviously shortened in the 
first form by the length of the connecting-rod, and in its 
second form by the length of the piston-rod. In the first form 
the cylinder lies between the cross-head and the crank, and in 
the second form the crank lies between the cylinder and the 
cross-head. Many vertical blowing-engines belong to the first 
class so far as their steam part is concerned (Fig. 13), and also 
some of the types of horizontal air-compressors (Fig. 14). 

15. Engines Classified by the Position of the Cylinder- 
axis. — The exigencies of location or use frequently determine, 
outside of any preference for one particular arrangement, 
whether an engine shall have the axis of its cylinder horizon- 
tal, vertical, or inclined. Three classes of engines result from 
these differences of the arrangement of the cylinder-axis, each 
of which offers advantages and disadvantages of its own. 

16. The Horizontal Engine. — The horizontal arrange- 
ment of the cylinder-axis is by far the most usual position for 
factory or mill engines, and for power plants where room or 
floor-space is not the governing condition (Fig. i). 

The advantages of the horizontal arrangement are: First, 
convenience of access from the ground-level to every point of 
the engine mechanism. This is a convenience both in opera- 
tion and in repair. Second, the weight of the engine is dis- 



THE MECHANISM OF ENGINES. 



27 




W 



28 MECHANICAL ENGINEERING OF POWER PLANTS. 




THE MECHANISM OF ENGINES. 



29 




30 MECHANICAL ENGINEERING OF POWER PLANTS, 

tributed over a large area for its support. This is of consider- 
able moment where earth must be depended on to support 
the foundation, and becomes a critical condition of design 
for boat-engines, where the light draught imposed by shallow 
water compels a shallow and therefore flexible or deflecting 
hull structure. This is a notable peculiarity of the practice 
of engine design for the western rivers of America and for the 
shallow waters of the British Colonies. Third, the foundation 
itself does not require to be so massive to hold the engine 
still, and to keep its frame from jar or vibration. The first 
of these is usually considered the notable advantage of the 
horizontal engine. 

The disadvantages of the horizontal engine are: First, that 
the action of gravity on all masses of the mechanism produces 
a friction which is absent in a vertical cylinder. The spring 
appliances of the piston which are intended to make it fit the 
bore steam-tight require to have strength sufficient to support 
the solid piston in the axis of the cylinder and prevent a wear- 
ing of the stuffing-box down on the lower side. The action 
of these springs increases the friction. 

Secondly, due to either of these actions or to both, it. is 
supposed there is an excess of wear on the bottom elements 
of the cylinder which causes the bore to wear oval with the 
long axis vertical. 

While the tendency of horizontal cylinders to wear oval 
is undeniable, it is a fair question whether this may not be 
caused rather by the springing of the guides and a flexing of 
the frame than by the action of gravity upon the piston; and 
in many stationary engines bolted to foundations the change 
of shape due to expansion by heat not infrequently so deranges 
the alignment of the engine as to cause the cylinder to wear 
unequally. The tendency to wear is also diminished by having 
the area of contact between the piston and its bore large 
enough so that for a given weight of piston the pressure per 
unit of area becomes so far reduced as to make wear inappre- 
ciable. A great gain is further secured by so selecting the 
material for the cylinder-casting that it may resist wear by 



THE MECHANISM OF ENGINES. 31 

abrasion. The difficulty from wearing is further diminished 
by the practice quite usual with heavy pistons of prolonging 
the piston-rod out through the back or head end through a 
stuffing-box. This not only supports the weight of piston, 
but serves to guide it effectively in the axis of the cylinder. 

17. The Vertical Engine. — The advantages belonging to 
the vertical arrangement of the cylinder-axis are the avoidance 
of cylinder-friction and unequal wear, which are the disadvan- 
tages of the horizontal engine. But of more moment than 
these is the diminished area in ground-plan which is entailed 
when the length of the engine is up and down. This condi- 
tion has made the vertical engine practically universal for 
screw-propelled ships which are not primarily war-vessels, and 
has given to this arrangement its wide distribution in crowded 
power plants in cities where ground is costly (Fig. 15). 

The objections to the vertical engine are: First, the effort 
on the crank-pin is greater when the weight of the mechanism 
is acting downwards with gravity than it would naturally be 
when the effort of the steam has to lift the same weight against 
gravity upon the up-stroke. This must be counteracted, 
because otherwise the effort upon the pin, and therefore the 
speed, would be irregular. It can be done either by counter- 
weighting the crank on the side opposite to the pin to which 
the reciprocating parts are attached, or by means of a steam- 
cylinder whose area shall be so calculated that the pressure of 
the steam shall just neutralize the weight to be overcome; or 
the distribution of steam to the heavy end of the cylinder can 
be adjusted so as to develop more effort at that end than at 
the other. The second difficulty is that in a large engine the 
different parts of the mechanism will be upon different levels 
or stories, increasing the number of men required to handle or 
superintend it. Third, the engine is not so completely and 
inflexibly secured to its foundation and a deeper foundation is 
thereby required, or an unequal settling of such foundation 
will occur, if the concentrated load is not sufficiently widely 
distributed. Fourth, when the piston-rod protrudes from the 
bottom head of such vertical cylinder the combined effect of 



32 MECHANICAL ENGINEERING OF POWER PLANTS. 

capillary action and gravity upon the condensation which takes 
place around the rod in the stuffing-box and upon the cover 




make it very troublesome to make the stuffing-box tight 
enough to prevent leakage of water. 



THE MECHANISM OF ENGINES. 



33 



i8. Inverted Vertical Engines. — The cylinder of a verti- 
cal engine can be arranged to have the cylinder supported upon 
suitable frames above the crank and shaft, or the cylinder may 
be below, and the crank and the shaft above it. The arrange- 
ment with the cylinder overhead is by far the most usual and 




Bradley ^ Poatea, Engr'e, jV. F. 

Fig. i6. 

is known as the inverted vertical type. The general advan- 
tage of this arrangement is that the moving reciprocating 
parts, which are those whose inertia or living force must be 
taken up by solid connection and for which the crank-pin must 
provide, are held to the ground through the crank-shaft di- 



34 MECHANICAL ENGINEERING OF POWER PLANTS, 

rectly secured to the foundation. The cyb'nder has nearly the 
same strain on it as the crank-pin, but these strains are trans- 
mitted through the elastic cushioning action of the steam. 




The cylinder furthermore, is not a moving part. Fig. i6 
Illustrates a typical inverted vertical engine of this sort. 

For certain uses the inverted vertical arrangement is spe- 
cially adapted by reason of the location of the engine-shaft 
near the base. It is this condition which has made this the 
typical marine engine, Fig. 17; but it is also adapted for 



T HE MECHANISM OF ENGINES, 



35 




Fig. i8. 



36 MECHANICAL ENGINEERING OF POWER PLANTS. 

driving directly-coupled dynamo-machines, rolling-mills, and 
the like where the vertical arrangement is either necessary or 
preferred (Fig. 15). 

It will again be found the most convenient arrangement 
for water-works pumping-engines where the level of the 
water in the well or source from which the pump draws is 
either some distance below the general surface of the ground or 
is liable to wide fluctuations. Furthermore, where the pump- 
ing organ is a plunger of considerable weight or length it will 
naturally be arranged to travel vertically and the steam-cylin- 
der which drives it will be inverted vertically above it (Fig. 1 8). 

19. Direct Vertical Engines. — When for any reason the 
shaft to be driven directly by the engine stands at a height 
above the ground, the direct vertical engine will permit the 
weight of the cylinder to be supported directly upon the 
foundation, while the piston-rod passing out through the top 
of the cylinder conveys the motion of the piston to the shaft 
overhead. This arrangement is very little known in America 
except for pumping (Fig. 19), and with one exception has 
been restricted to factory practice at slow rotative speeds. In 
European shops such engines are often bolted to the wall, and 
are then called wall engines. Where a vertical engine has been 
desired and the inverted type disapproved, either the back- 
acting design has been chosen (Fig. 13), or use has been made 
of the advantage offered by some of the beam mechanisms. 

20. Inclined Engines. — It is sometimes convenient to 
arrange the engine-cylinders so that their axis is inclined to 
the horizon. This is the condition which is frequently met 
in marine practice where the propelling is done by side wheels 
whose diameter determines the height above the water of the 
shaft which carries them. 

It is furthermore desirable to keep the centre of gravity as 
low as possible, and therefore to bring the weight of the 
cylinder or cylinders near the keelson. This has made the 
inclined engine a favorite type for light-draught vessels in 
Europe and for ferry-boat practice in American Abaters (Fig. 
20). The frame of such engines is a comparatively light 



THE MECHANISM OF ENGINES. 



n 




Fig. 19. 



38 MECHANICAL ENGINEERING OF POWER PLANTS. 




THE MECHANISM OF ENGINES. 



39 



structure. For stationary practice the inclined engine has 
been almost limited either to very small designs or to the 
practice of pumping-engines. For small designs (Fig. 2i) 
it permits the use of the large-diameter fly-wheel without 




Fig. 21. 

the necessity of a pit below the general level, and for pump- 
ing-engines it permits a symmetrical arrangement of two 
cylinders or four cylinders with the pumps below them on 
the same rods, and yet the engine does not extend over so 
great an area of ground-plan. In the design exhibited in 
Fig. 22 it will be observed that by the arrangement of the 



40 MECHANICAL ENGINEERING OF POWER PLANTS. 

two cylinders the practical result of having two cranks quar- 
tering (see par. ii) is secured with only one crank-pin. 

The inclined engine has both the advantages and disadvan- 
tages of the horizontal and vertical engines; and while it does 




not suffer as much from the disadvantages, neither does it 
benefit as much from the advantages. The piston is apt to 
wear the bore seriously from a tendency to dig into the metal 
at upper and lower corners. 

21. Combined Horizontal and Vertical Engines. — A 
design of engine has been used for pumping or compressing 



\ 



\ 



THE MECHANISM OF ENGINES. 



41 



service in which the steam-cyUnder is arranged with vertical 
axis, and the pumping or compressing cyHnder is horizontal 
or inclined. In a form of ammonia-compression refrigerating 
machine this arrangement is reversed, and the steam-cylinder 
is horizontal and the ammonia-cylinder is vertical (Fig. 24). 




Fig. 24. 

This arrangement is designed to quarter the cranks of the 
respective cylinders, so that the maximum effort of the steam 
end should concur with the greatest resistance. It can also 
be made an arrangement for a beam-engine mechanism (see 
par. 22), securing the advantages of the vertical steam-cylinder 
and yet so arranging the water-cylinders as to permit con- 
venient access to valve-chambers and convenient approach for 
the suction-water. 

22. Direct-acting and Beam Engines. — In the typical 



42 MECHANICAL ENGINEERING OF POWER PLANTS. 

• 

mechanism presented in Fig. i the mechanism by which the 
motion of the piston is transmitted to the revolving crank is as 
direct as is possible. Engines in which the end of the piston- 
rod acts thus directly upon the pin of the crank are called 
direct-acting engines. 

The term direct-acting is also used to express the opposite 
of back-acting, and is again used in steam-pump practice to 
denote the type of pump in which there is introduced no 
rotary mechanism with shaft and fl)7-wheel weight, the steam- 
piston acting directly upon the pumping-piston. In this latter 
sense it is synonymous with the term non-fly-wheel pump, 
and in the first case it is synonymous with forward-acting 
engine to distinguish it from back-acting. It is unfortunate 
that the same term should have so many different meanings, 
because in the sense in which it is desired to use it here the 
distinction is to be drawn between direct-acting engines like 
Fig. I and those in which the effort in the cylinder reaches- 
the crank-pin indirectly through a beam. 

23. Beam -engines. — Since the earliest steam-engines 
were designed to operate the rods of mine-pumps, it was con- 
venient to locate the cylinder at a little distance back from the 
mouth of the shaft, and to transmit the motion of the piston 
to the rod which went down the shaft or pit by means of a 
pivoted lever or beam. This beam was usually of wood 
pivoted at the centre on convenient bearings, which were in. 
most cases supported upon a masonry wall. When the func- 
tion of the engine changed from that of pumping to the con- 
tinuous driving of a revolving shaft the general design was 
only modified by connecting the outer end of the beam by a 
suitable connecting-rod to the crank-pin of the revolving shaft, 
and it seems probable that the term pitman often and prop- 
erly attached to this organ of a beam-engine mechanism is a 
survival of the early mining term. The earliest steam-engines 
in America for marine use were beam-engines, and the prefer- 
ence of many skilled designers of side-wheel vessels for this 
type of mechanism shows that there are valid reasons for its 
popularity. 



THE MECHANISM OF ENGINES. 43 

The advantages of the beam-engine mechanism are as 
follows: 

First, the steam-cylinder can be vertical (pars. i6 to 1 8.) 

Second, the cylinder and its weight can be kept low down 
and the shaft may also be directly attached to the bed-plate 
near the foundation. 

Third, a long stroke for the piston is possible and yet not 
too much space in ground-plan consumed. This is a great 
advantage in side-wheel practice and in pumping. In both 
these cases the number of revolutions or the number of 
reciprocations of the piston must be kept low, yet it is 
desirable that the piston-speed LN (par. 6) should be made 
high in order that the engine may be powerful. The beam- 
engine attains these results in a satisfactory way. 

Fourth, the beam-engine secures a flexibility in the align- 
ment of the cylinder-axis in its relation to the axis of the 
shaft. Tliis is specially desirable for vessels of light draught 
whose hulls cannot be made absolutely rigid. 

Fifth, for engines specifically designed for pumping, and 
particularly where several steam-cylinders and work-cylinders 
are features of the design, the beam construction furnishes 
convenient points of attachment for these various organs. 

Sixth, where valid reasons demand that the steam-cylinders 
be vertical and the work-cylinders horizontal or inclined, 
while their motion shall be limited and controlled b}^ a revolv- 
ing crank and fly-wheel, the beam principle lends itself to 
attainment of this result. 

It is probable that the union of high piston-speed with 
slow rotative speed, and the advantages which are secured by 
the combination of these two features in a flexible arrange- 
ment, are the cogent reasons for the widespread acceptance of 
the beam mechanism. 

24. Structure of Beam-engines. — Fig. 30 illustrates a 
typical arrangement of an American river-boat beam-engine 
of the period 1850 to 1875. The type was practically fixed 
by the late Charles W. Copeland, and the sketch shows the 
beam supported on a frame of wood which has been variously 



1 



44 MECHANICAL ENGINEERING OF POWER PLANTS. 

called the gallows-frame or the A-frame, from its shape. It 
will be seen to have been well braced by wooden knees. The 
modern frame is of steel worked up into box-girder forms, 




Fig. 30. 

securing thereby greater rigidity and less weight than was 
required in the wooden frames which they have displaced. 

The beam itself in early practice was a cast-iron girder 
with the metal of the flanges so disposed as to secure the 



THE MECHANISM OF ENGINES. 45 

greatest strength and stiffness with the least weight. This- 
gave to the beam the form of two semi-parabolas back to 
back, meeting over the centre. The greater lightness attained 
by using wrought iron for tension elements of the beam caused 
the open-work or lozenge beam to be early adopted by 
American designers. Its first use is usually attributed to 
Stevens. The solid wrought-iron forged diamond or lozenge 
transmits the alternating push and pull of the piston, and the 
cast-iron centre keeps the beam in shape and is exposed to 
compression only. 

The cross-head at the upper end of the piston-rod either is 
guided in a straight-line path or is steadied by a linkage or 
parallel motion. The linkage is less usual. Two short con- 
necting-rods connect the cross-head to the beam, one on each 
side of the latter to cause a symmetrical application of the 
force. Great care is necessary in the practical handling of 
these short connecting-rods, as they wear at the bearing 
surfaces; since if they are permitted to become of unequal 
length a serious cross-strain is brought upon the cross-head, 
and a twisting strain upon the beam. 

At the outer or crank end of the beam depends the long 
connecting-rod or pitman. It requires to be long when the 
crank is long, and it is therefore usual to brace and truss it 
with light steel tension-rods and king-posts, so that in its 
amplitude of swing its own mass should not have a tendency 
to make it bend. 

Fig. 31 shows the form which the beam-engine may be 
made to take for war-ship conditions and where a short 
stroke and rapid revolution of the screw-shaft running length- 
wise of the vessel are the conditions to be met. The vessel 
is a twin-screw cruiser, and the engines are arranged right and 
left athwart ship. There is space between the two shafts for 
the vertical cylinders and the beam frame, and yet the whole 
engine mechanism is below the water-line. Fig. 32 shows the 
convenience of the beam mechanism when pump-plungers and 
connecting-rods are to be provided for as well as the steam- 
cylinder connections. While the inclined-cylinder design 



46 MECHANICAL ENGINEERING OF POWER PLANTS, 




THE MECHANISM OE ENGINES. 



47 




swG cicmncH 






48 



MECHANICAL ENGINEERING OF POWER PLANTS, 



permits the straight descent of the plunger-rods, it can readily^ 
be seen that a successful design could as easily have been 
made by having the cylinders vertical and attached to a 




longer beam, leaving space nearer the centre for the attach- 
ment of the plunger-rods, and one on each side could have 
been used. It is an advantage to give a long stroke to the 
steam-cylinder to secure high piston-speed. 



THE MECHANISM OF ENGINES. 



49 



Fig. 33 shows a modern type of beam-engine in which 
the cyHnders are horizontal and the angular motion of the 
beam is on each side of a vertical centre-line instead of a hori- 
zontal as hitherto. The pump-plunger is here continuous 
with one of the piston-rods and the beam serves to transmit 
and equalize the work of the other cylinder and the regu- 
lating effect of the fly-wheel and crank. 

Fig. 34 shows a type of triangular beam-engines which 




^^^<*. 



Fig. 34. 

come about when the axes of the cylinders are parallel to each 
other and the fly-wheel shaft in line with neither; in Fig. 35 
the beam is in line with the steam-cylinder, and in Fig. 36 
the beam loses its linear or conventional shape. 

25. Objections to the Beam-engine. — The Side-lever 
Engine. — Objections to the beam-engine are: 



50 MECHANICAL ENGINEERING OF POWER PLANTS. 




THE MECHANISM OF ENGINES. 



51 



First, those attaching to a transmission of the work through 
so many joints indirectly to the crank-pin.. Secondly, the 
objection in marine practice to having the weight of the 




, beam so far above the centre of gravity of the hull. Third, 

the objection in war-ship practice to having a vulnerable part 

.| of the mechanism exposed and a part whose destruction is fatal. 



52 MECHANICAL ENGINEERING OF POWER PLANTS. 



These objections gave rise at an early date to the adoption 
of the back-acting principle to beam-engines with a double 
beam pivoted below on each side of the frame. From this 
double beam or side lever the connecting-rod or pitman rose 
to the level of the main shaft above the beam. This was the 
type known as the side-lever engine, and was in very general 
use up to the time when the introduction of the propelling 
screw displaced the side wheel for ocean service (Fig. 37). A 




(I 



Fig. 37. 

combination of back-acting and beam-engine mechanism is to 
be found in certain monitor engines, where the beam became 
more like a rock-shaft, or had only one side to it, but in 
different planes. Fig. 38 shows the engine of the U. S. 
monitor Monadnock, embodying this peculiarity. 

26. The Rotary Steam-engine. — By reference to par. 9 
it will be seen that it is possible to apply the expansive energy 
of steam directly to produce rotation of the engine-shaft. 
The piston instead of reciprocating in a straight cylinder has a 



THE MECHANISM OF ENGINES, 



53 




54 MECHANICAL ENGINEERING OF POWER PLANTS. 

rotary or revolving motion around an axis which is usually 
the axis of the shaft. The area on which the steam presses is 
really an enlargement of the crank-pin properly modified for 
this purpose. The piston is usually a plane surface which fits 
what must be called the cylinder steam-tight at its edges, 
and the path of the piston is a continuous curve, in which 
the centre of effort upon this piston moves in a given time. 

The pressure coming to the cylinder through a pipe must 
exert its effort upon the rotating piston or pistons, and must 
then be allowed to escape. There must therefore be the 
steam-pressure on one side and the pressure of the atmosphere 
as nearly as may be upon the other side, and this condition 
must be continuous at all points of the rotation. Provision 
must therefore be made in the design to separate the steam 
and exhaust sides of the rotating piston, and this must be 
done by some device which shall not interfere with the con- 
tinuous rotation of the pistons. The device or appliance used 
to separate the inlet and exhaust openings of a rotary-engine 
cylinder has been conveniently called the abutment, and every 
successful rotary engine must exhibit the two organs of abut- 
ment and piston. While the number of designs of rotary 
engines is very great, they may be roughly grouped into two 
classes: first, where the abutment and piston are continually 
interchanging their functions; and second, where the abut- 
ment is always abutment, and pistons are always pistons. 

27. Rotary Steam-engines in which Pistons and Abut- 
ment Alternate their Functions. — Fig. 39 illustrates two 
forms of engine constructed upon this principle. In both 
cases the steam enters at the bottom and exerts its pressure 
upward upon the surfaces exposed to its action. It will be 
seen that a full pressure of steam is exerted on the lower part 
of the right-hand piston, while the upper part has pressing 
against it only the atmospheric pressure which prevails in the 
exhaust outlet B. The function of the left-hand piston C in 
the present position is simply that of preventing the direct 
passage of steam from the inlet A to the outlet B, without 
producing rotative effect. C is therefore the abutment. The 



THE MECHANISM OF ENGINES. 



55 



steam-pressure therefore turns the shaft of the piston D in the 
direction opposite to that of the hands of a watch, while the 
piston C turns in an opposite direction, or clockwise, from its 
connection outside the cylinder by means of gears and because 



THE engine:. 




there is a slightly greater area at the left hand receiving the 
steam-pressure than there is at the right. When the shaft and 
pistons have made a quarter-revolution their respective posi- 
tions will be reversed. C will be the driving piston and D 
the abutment, and so these two organs will alternate their 



56 MECHANICAL ENGINEERING OF POWER PLANTS. 

functions, each serving in each capacity twice in a revolution. 
The profile of these pistons must be circular and trochoidal 
curves, that they may roll upon each other and in contact with 
the outer casing without permitting leakage. They must also 
prevent leakage at their ends between the flat heads of their 
casing. Steam-tightness is secured in the two designs shown, 
by different methods. Against the cylindrical parts of the 
casing packing-strips are used in both designs which are forced 




Fig. 40. 

outwards by springs acting radially. The shape of the strips 
must be such that when the piston leaves the casing towards 
the middle the strips shall not drop out. For the packing 
againsc flat surfaces one design uses radial strips similarly 
pressed against the flat heads by springs, and the other 
depends upon counterbored holes drilled a short distance 
apart, parallel to the axis within which condensation and 
lubricant will be caught, which will serve by their capillary 
action to prevent any considerable escape of live steam. 



THE MECHANISM OF ENGINES. 



57 



28. Rotary Engine with Persistent Function of Piston 
and Abutment. — Fig. 40 illustrates the simplest type of 
rotary engine in which piston and abutment continuously dis- 
charge the function of each without interchanging them. The 
steam entering at the inlet A is prev^ented from crossing to 
the outlet B by the steam-tight contact of the abutment C 




Fig. 41. 

; with the casing and the piston D. Steam, therefore, acts to 
produce rotation of the piston Z) in a direction contrary to 
that of the clock-hands, because there is less pressure behind 
the lower part of it than there is in front of it, and therefore 
the shaft has a continuous motion. Fig, 41 illustrates a type 
in which the abutment is the continuous ring separating the 
inlet and the outlet at the point ^4, and compelling the steam 
to take the path between the abutment-ring and the outer 



58 MECHANICAL ENGINEERING OF POWER PLANTS. 

casing and exert its pressure upon those surfaces of the 
pistons /^ which protrude through the abutment-ring in radial 
slots. In this design we have three pistons carried upon three 
arms of the spider which is secured to the revolving-shaft, and 
the abutment-ring being out of centre with that shaft, permits 
the pistons to pass the separating portion A. As shown in 
the cut, the controlling valve stands in its central position so 
that if moved to the left the steam will follow as shown by 
the arrows and the pistons and shafts will rotate clockwise. 
If the valve be moved to the right steam will enter at the 
left-hand opening, producing a rotation of the piston anti- 
clockwise and the steam will escape into the exhaust-passage 
through the hollow in the valve from the right-hand port. 
Fig. 42 shows another form of ring-abutment rotary engine. 




Fig. 42. 

It will be apparent that the engine can be reversed in 
principle and become a rotary pump by applying power to 
the shaft by outside mechanical means and admitting water 
through the passages with which the steam enters in the rotary 
engine. This convenient peculiarity has given rise to a. 
popular form of steam fire-engine, in which the steam and 
water pistons are arranged on parallel shafts properly geared 
together. Such an engine requires no valves on its water end^ 



THE MECHANISM OF ENGINES. 59 

and the water used can be full of impurities and solid matter 
without great inconvenience. 

29. Advantages of the Rotary Engine. — The arguments 
to be urged in favor of the rotary-engine principle are so many 
that the skill of innumerable inventors has been continuously 
directed towards their design. Among other advantages are: 

1. The effort of the steam is applied directly without 
intervening mechanisms for conversion of the motion. This- 
avoids their attendant friction, their costly fitting, and proba- 
ble lost motion. 

2. There being no reciprocating parts, there is no inertia to 
be overcome at the beginning of the stroke, with the attendant 
consumption of energy required to accelerate them. 

3. The engine has no dead-centre, but will start from rest 
in any position. 

4. Absence of reciprocating parts makes it easy to run the 
shaft at the highest speed. This has attracted designers of 
steam-driven dynamos to use this type of engine. 

5. The engine becomes very compact from the absence of 
converting mechanism, so that it occupies, little room. 

6. The engine has either no valve-gearing, or that which 
it has is of the simplest character. 

7. These features, and the absence of expensive mechanism, 
make the engine cheap to build and therefore usually cheap 
to buy. 

8. Absence of reciprocating-rods and dead-centres results 
in a construction in which the presence of condensed steam 
in the cylinder does no harm. It does not stop the engine 
from turning, it cannot endanger the cylinder-casting, the 
engine can be started, even if under water, by simply opening 
the valve which admits pressure to it; it will start with solid 
water. 

9. Its incased construction and the above peculiarity par- 
ticularly adapt it for out-door service and exposed places. 
Weather does it no harm, and its protection from outside 
injury makes it a serviceable quarry motor. 

10. It requires no skill to handle it. If constructed to be 



60 MECHANICAL ENGINEERING OF POWER PLANTS. 

reversible as in Fig. 41, it can be reversed from a distance by- 
simple rope and weight. 

30. Disadvantages of the Rotary Engine. — The objec- 
tions to the rotary engine are both practical and inherent. 
The practical objections belong to the difficulty of satisfac- 
torily packing surfaces which do not move through equal 
spaces in equal times. Those parts farther from the axis move 
through a longer path in a revolution than those nearer to 
the axis. The wear from abrasion is therefore greater at one 
part than another. When the packing-strips have become 
somewhat worn, leakage ensues, and a noisy rattle from loose- 
ness of the fits. A second practical difficulty is the expense 
connected with proper lubrication of such engines, and the 
difficulty of taking care of excess of oil rejected by the 
exhaust. If efficiently lubricated, they consume an excessive- 
amount of oil. 

The inherent objections to the rotary engine are: 

1. The presence, in the volume to' be filled by live steam 
from the boiler, of an excessive waste space which has to be 
filled by steam at each revolution, which steam is exhausted 
without doing all the work there is in it. This corresponds 
in reciprocating engines to an excessive clearance. 

2. The very continuity of the action of the steam upon 
the rotating pistons precludes the possibility with the single 
rotary engine of working the steam expansively, so that when 
the steam leaves the motor it shall have become largely 
reduced in temperature and pressure by doing work with 
increase of its initial volume. The expansion is from the 
boiler and the water in it, and not from the actual volume 
received by the engine for the work of one stroke. In other 
words, the rotary engine is a non-expansive engine. These 
two difficulties make the rotary engine uneconomical. 

3. It is difficult to design the rotary engine for large 
horse-powers: 

First, because the structure becomes inconvenient the 
moment that large areas are desired, so as to make a value of 
PA in the horse-power formula a large factor; second, because 



THE MECHANISM OF ENGINES, 6 1 

it becomes difficult to secure the condition of high piston-speed 
in feet per minute unless the diameter of the casing be made 
so large that the difficulties both practical and inherent 
become nearly insurmountable and the advantages of the 
rotary principle are sacrificed. 

The economy which a single rotary engine cannot secure 
from its inability to work the steam expansively has been 
sought and secured in a degree by arranging rotary engines in 
series upon a shaft, so that the steam rejected from number 
one engine becomes the driving steam for motor number two 
of larger volume. By this means the steam when rejected is at 
more nearly the pressure and temperature of saturated steam 
at atmospheric pressure than can be attained with the single 
rotary engine. 

31. The Steam-turbine. — Closely resembling the rotary 
steam-engine in its feature of direct application of power are 
the forms of the steam-turbine. They are of several different 
types, but all depend upon receiving the living force of steam 
escaping through a nozzle from a high pressure to a lower 
upon curved vanes or buckets. These vanes receive the 
impact of the rapidly moving steam and utilize its energy, 
the shape of the buckets being such that when the steam 
leaves them it has only sufficient velocity to escape into the 
exhaust-pipe so as to be freed from the motor. The three 
best known steam-turbines are Dow's, Parson's, and the 
Delaval, of which Figs. 43 to 46 present views and sections. 

32. Square-piston Engines and Disk-engines. — A form 
of engine has been designed to secure compactness w^ith direct 
application of the steam-pressure upon the crank-pin, which 
has been called the square-piston engine from the shape of 
the cylinder and the double pistons in the head. It will be 
seen from the cut Fig. 47 that there are two sets of recipro- 
cating pistons, one in a horizontal plane and the other in a 
vertical plane. Each piston is really a part of the frame which 
slides steam-tight in the casing which it fits. The double 
motion enables the components of rotary motion to be pro- 
vided for in the reciprocating frames upon which the steam- 



62 MECHANICAL ENGINEERING OF POWER PLANTS. 



1 




Fig. 44. — Section of Dow Turbine. 



THE MECHANISM OF ENGINES. 




J 



79-78- 



1\ 



r 



04 MECHANICAL ENGINEERING OF POWER PLANTS. 

pressure acts directly. It is not difficult to make such pistons 
serve the purpose of their own valves, so that an engine of this 




PLAN 

Fig. 46. — De Latal Turbine. 




Fig. 47. 

construction offers many of the features sought by the rotary- 
engine design and yet permits expansive working. 

What are called disk-engines are of two great types. The 
first might properly be called a vibrating-piston engine or 



THE MECHANISM OF ENGINES. 



6s 



sometimes a pendulum-engine, such as is shown in Fig. 48. 
It will be seen that a flat flap or disk does not revolve through 
the complete circle, but only through a relatively small arc 
from whose motion outside of the cylinder proper the outer 
connecting-rod will convert vibratory into rotary motion as in 




the beam-engine. This design was proposed many years ago^ 
by Captain Ericsson. 

A more usual form of engine in which a vibrating-pressure 
organ forms a part is that presented in Fig. 49. This shows 
a disk B against whch press six single-acting pistons which. 



^66 MECHANICAL ENGINEERING OF POWER PLANTS. 



receive steam upon their right-hand ends only. The left-hand 
ends bear upon the vibrating disk, which receives a rolling 
vibrating motion around a spherical joint at D. It will be 
seen that the axis F of the rolling disk will describe a cone. 
As the disk revolves, its conical motion can be made the 
motion which turns the crank G of the shaft H of the engine. 
The valve of the engine is of the simplest construction, since 




FiCx. 49. 

it can be a simple disk which travels with an eccentric motion 
around an eccentric /. The form of mechanism described by 
Rankine under the name of Hunt's Z-crank engine is a 
design of similar character (Rankine's ** Machinery and Mill 
AVork," edition of 1876, page 273). 

33. Sundry Special Mechanisms. — A final class must be 
made in order to include certain forms of mechanisms which 
have been proposed and received a certain amount of develop- 
ment and which are departures from the typical mechanisms 
discussed hitherto. The first will be a form of three-cylinder 



THE MECHANISM OF ENGINES. 



67 



engine (Fig. 50), which is usually a trunk design and single- 
acting upon three cylinders in succession. This arrangement 




eversing engine. 
Fig. 50. 

II produces an equal turning effort with little or no fly-wheel 
weight, but will obviously be limited to relatively small sizes. 



68 MECHANICAL ENGINEERING OF POWER PLANTS, 



A four-cylinder design with the axes either parallel or at 
right angles in pairs and with the cranks quartering is presented 
in Figs. 51 and 52. It will be seen that these offer the same 
advantages for small sizes as the three-cylinder arrangements. 




Fig. 52. 

A design of engine aiming to balance the reciprocating 
weights around the crank-pins upon one shaft is shown by 
Fig- 53- It will be seen that the upper piston will always be 
ascending when the lower one is descending, and vice versa^ 
equalizing the effect of gravity and rendering it unnecessary 
to balance the living force of such reciprocating parts by a 
revolving counterbalance on the shaft. While the figure shows 
the design of a vertical engine, the same principle holds and is 
applicable in horizontal arrangements. A form of four-cylin- 
der compound locomotive has been proposed which embodies 
these features of balancing the reciprocating parts without 
extra revolving weight. 



THE MECHANISM OF ENGINES. 



69 




DESCRIPTION. 

A— The high pressure cylinder, 

B— The low pressure cylinder. 

C— The steam chest. 

D— The receiver. 

E— The exhaust passage. 

a— The high-pressure piston. 

b— The low pressure piston. 

c— The piston valve. 

d-The valve casing. 

e— -The reversing lever. 

F— Crank-shaft. 




Fig. 53. 



CHAPTER III. 
CLASSIFICATION OF ENGINES BY THEIR USE OF STEAM. 

34. Introductory. — The previous chapter has discussed 
the different classes of engines from the standpoint of their 
mechanism by which the expansive effort of the steam pro- 
duced rotation at the crank-shaft. It is obviously possible to 
use the steam according to any of the methods to be discussed 
in this chapter with any of the arrangements of mechanism 
discussed in the previous chapter, thus making a large number 
of combinations possible. The five classes of engines to be 
discussed in the next chapters are as follows: 

1. High-speed, low-speed, and moderate speed of rotation 
or of piston. 

2. Single- and double-acting. 

3. Expansive and non-expansive. 

4. Condensing and non-condensing. 

5. Single or compound or multiple expansive. 

35. High-speed Engines. — It will be recalled, par. 6, that 
the horse-power of an engine-cylinder is given by an equation 
of the form 

PALN 



H.P. = 



33,000 



It will be apparent that where the given horse-power is to be 
secured and the mean pressure P in the above formula is 
fixed by convenience or for other reasons, both A and L can 
be diminished as N increases, which denotes the number of 
reciprocations of the piston in the cylinder, which number is 
twice the number of revolutions in the assumed type. Where ^ pa 
this practice ie followed the engine has a high rotative speed ty 

70 



ENGINES CLASSIFIED BY THEIR USE OF STEAM. /I 

or makes a large number of revolutions per minute. The 
consequences of this are: 

1. The engine has a small cylinder-volume because it fills 
that volume frequently each minute. 

2. The small cylinder-volume both in length and diameter 
means an engine light in weight. 

3. A short length of cylinder means a small crank-arm, a 
short connecting-rod, and an engine short in length. These 
three conditions are the same as to say that to increase N 
diminishes both weight and bulk with a given power. P also 
has no weight. 

4. When the engine makes a high number of revolutions 
per minute each revolution is made in a fraction of a second, 
and consequently a variation of either effort or of resistance is 
more promptly met, and is less noticeable as compared with 
the mean effort or resistance of any given minute 

5. The regulating mechanism partaking of the rapid 
rotative motion produces its effect to equalize effort and 
resistance in a less interval of time than with the slower- 
moving types. 

36. Low-speed Engines. — It happens frequently thai the 
resistance to be overcome imposes a limit upon the number 
of reciprocations or revolutions desirable per minute. This 
condition is met in pumping-engines, blowing-engines, and 
paddle-wheel marine-engines, and is one reason why these 
engines appear usually of large dimensions. It will be appar- 
ent, however, that the product LN oi the formula representing 
the feet through which the effort of the steam moves in one 
minute, and which is called the piston-speed of the engine,, 
can be made large without increasing N. This results in 
Avhat are called long-stroke engines, of which examples have 
appeared hitherto in the types of marine beam-engines. 

The advantages of the low rotative speed with high piston- 
speed are the avoiding of the disadvantages belonging to the 
short-stroke high rotative-speed engines discussed in a previous 
paragraph. The disadvantages of the high rotative-speed, 
types are: 



J 2 MECHANICAL ENGINEERING OF POWER PLANTS. 

1. The rapid alternating of admission and suppression of 
steam through the ports to the cyHnder compel large port- 
areas in the design of such engines. 

2. The rapid motion of the piston compels a generous 
allowance at each end between the piston at its dead-centres 
at the heads of the cylinder. 

These two conditions create a clearance-volume of the 
cylinder at each end which is filled many times a minute with 
steam which escapes at the exhaust without doing work. The 
clearance-volume will be the area of the piston multiplied by 
the allowance length, which is usually a small fraction of an 
inch. That length and volume will be a greater percentage 
of a short cylinder than the same length and volume will be 
in a long cylinder, and it is filled and emptied more frequently 
in the high-speed engine. 

3. Where the stroke is short the surfaces traversed are 
traversed more frequently and therefore the wear per unit of 
surface will be greater. This holds true for wear at all rub- 
bing surfaces. 

4. The concentration of friction and pressure upon small 
areas frequently in action upon each other compels very close 
attendance upon such engines, because heating and abrasive 
wear goes on with great rapidity when once allowed to begin, 
from the very circumstances of the case. These two condi- 
tions increase the possibility of expense for maintenance and 
repairs for this class of engines. 

5/ These conditions of concentration compel lubrication 
of such engines to be copious to a wasteful degree for safety. 

6. The foregoing conditions compel a standard of work- 
manship in the matter of fitting, alignment, and provision 
for wear which make high-speed engines costly to build and 
successful only when very well made. 

These objections to the high rotative-speed steam-engine 
are the considerations which point to either a moderate or 
low speed of rotation as that to be desired when circumstances 
permit. 

37. Figures of Piston-speed in Feet per Minute. — Since 




tcr of Cylinder -.90" 

a of Stroke of Piston 10' 

jr of Pumps 2 

Working Barrel 36' 

j Auxilliary Barrel &t° 

i Stroke ....10 

Valves of the double-beat 

Mle-acting Air Pump 

ter of Air Pump 3' 

/I h of Stroke 5' 

jcj^it of centre of Beam above 

[Gf'o. 



■^TRUTHER^& COV^EMGR S, N.ar 

level of Floor 2b 3- 

Length of Beam between end 
centres - 30' 

Depth of Beam in middle 7'2" 

Average thickness of Web 0'6" 

Diameter of Air Chamber 6' 6i' 

Height of Air Chamber 25'4' 

" " " " above 

Floor 13'10' 

Total weight of Engine, Boilers 
and Appurtenances 440 Tons 



ENGINES CLASSIFIED BY THEIR USE OF STEAM. 73 

the product LN of the horse-power formula is made up of two 
factors, a very wide number of combinations is possible. 
When LN is expressed in feet and their product is less than 
500 feet per minute, the engine would be called a low- speed 
engine. Between 600 and 800 feet per minute is a moderate 
piston-speed, and above 900 feet is a high piston-speed. 
Many forms of valve-gear preclude the use of high rotative 
speed, and are best run at speeds not higher than 100 revolu- 
tions per minute. Engines for electric lighting with suitable 
valve-gear can be run above 200 revolutions per minute; 
locomotives usually exceed 300. Attempts to run engines of 
considerable size faster than 400 revolutions per minute have 
not been altogether satisfactory. 

38. Double and Single-acting Engines. — When the pres- 
sure of the steam is alternately exerted on the one side and 
the other of the piston, the engine is said to be double-acting. 
When that pressure is exerted on the one side only, to push 
the piston in one direction only, and some other force or 
stored energy is exerted to bring it back, the engine is called 
a single-acting engine. 

Historically the first engines were single-acting, having 
their cylinders open to the atmosphere on one side. The 
steam entered at the closed end and displaced the piston, was 
then condensed, leaving a vacuum behind, and atmospheric 
pressure forced the piston back to its starting-point. 

The single-acting engine is only half as powerful for a 
^iven cylinder-volume as the double-acting engine of the same 
size. It offers, however, certain advantages. 

39. The- Cornish Engine. — A form of pumping-engine, 
•single-acting in type, was early applied at mines in Cornwall, 
England, and has had a considerable popularity for water- 
ivorks uses and for deep-mine conditions — for the latter by 
reason of its convenient solution of the problem of massive 
■pump-rods. The Cornish engine appears in two forms. The 

li l>eam Cornish engine has a vertical cylinder from whose top. 
the piston-rod passes to one end of a beam pivoted at its 
centre, Fig. 60, to whose other end, (which in mine-pumps 



74 MECHANICAL ENGINEERING OF POWER PLANTS. 



usually hangs over the mouth of the shaft), are attached the 
pump-rods. The Bull Cornish, from the name of its first 
adapter, has the piston-rods coming out of the bottom of the 
vertical cylinder and directly attached to the pump-rods. 
This compels the cylinder to be located over the mouth of 
the shaft or above the plungers. In some French designs of 
Cornish engines the beam is placed below the cylinder, but in 
either arrangement of the beam-engine the working-stroke is 
the descending stroke of the piston in the cylinder, and in the 
Bull engine the working-stroke is the upward stroke. The 
Cornish pumping-engine has no fly-wheel, and depends for the 
control of its motion upon the resistance offered by the water 
and the combined effect of the admission and compression of 
the ste^m in the cylinder at the two ends of its traverse. 
40. Operation of the Cornish-engine Cylinder.^The 

cylinder of the Cornish engine has three valves 

^s(Fig. 6.): 

1. The inlet- valve (5), admitting steam. 

2. The exhaust-valve (Z^), allowing steam 
to escape, usually to the condenser. 

3. The equilibrium-valve (^), opening and 
closing a pipe or passage between the upper 
and lower ends of the cylinder above and 
below the piston when at the upper or lower 
end. 

The steam-valve and the exhaust-valve will 
° be at opposite ends of the cylinder, the 
1 steam-valve at the bottom of the Bull engine 
and the top of a beam-engine. The cycle of 
operation will be as follows: The massive pump-rods being 
at the bottom of their motion and the piston at the corre- 
sponding end of its cylinder, the steam-valve will be opened 
and the exhaust-valve opened while the equilibrium-valve 
remains closed. The pressure of the steam overcoming the 
weight of the rods, the piston will move and the rods will be 
lifted. The admission of steam will cease at such a point in 
the stroke as is indicated by calculation and experiment, in 




Fig. 61 



ENGINES CLASSIFIED BY USE OF STEAM, 7$ 

order to impart to the rods sufficient living force to carry 
them to the end of their stroke. The exhaust-valve will 
close before the piston completes its stroke, so as to shut in 
between the piston and the head of the cylinder sufficient 
steam to form an elastic cushion strong enough to arrest the 
piston before it strikes the head. 

Safety-catches or buffers were usually supplied in old 
engines to prevent this accident mechanically if the steam 
should fail to serve. 

The massive pump-rods being now at the top of their 
stroke, the third or equilibrium valve is opened, permitting the 
steam to pass through it on its passage to the other side of the 
piston so as to produce equilibrium of pressure on both sides. 
The weight of the rods causes them to descend, displacing the 
water to be pumped with a speed, which is controlled by 
the valves of the pump, and by the extent of the opening of 
the equilibrium-valve. Both steam- and exhaust-valve are 
closed during this equilibrium stroke, and the equilibrium- 
valve should itself be closed before the end of the stroke, so 
as to compress the steam between the piston and the head, 
cushioning the piston and filling all clearances with steam at 
inlet pressure. The cycle begins anew by the opening of 
the inlet- and exhaust-valves for the next stroke. It should 
be observed that the work of the Cornish cylinder is the lift- 
ing of the rods, and the pumping operation is performed by 
the descent of the lifted rods. In water-works engines 
where length of rod is lacking to overcome a considerable 
head of water, an extra weight of metal will be added to 
the necessary bulk of the water-plungers (Fig. 60). 

41. Cataract of the Cornish Pumplng-engine. — The Cor- 
nish pumping-engine requires a special mechanism to operate 
its valves. In common with all engines which lack a rotative 
shaft with fly-wheel and energy stored in it, it will come to 
rest at the end of its stroke with its valves closed and conse- 
quently will not reverse. 

The energy stored in a rotating fly-wheel will carry the 
engine past its centre and open the valves immediately for the 



76 MECHANICAL ENGINEERING OF POWER PLANTS. 







— 




p ^ 








•A 




m 










— - — -^ — ^ 


fc 






- 


A 


J 


-^ — h-^^ 


1 









— - 


— ^H-r^-j\ — 






-1^1 










M 





=TZ 


. 


, 



Fig. 62. 



reverse stroke. If it is desired to have an interval between 
strokes, the energy to open the valves must be stored in 
some other way. The most convenient and usual device for 
this purpose is to have a weight lifted by the working stroke, 
whose descent shall be controlled by the rapidity with which 

water will escape through an ori- 
fice whose size can be graduated. 
Fig. 62 will illustrate this device, 
which is usually called the cataract. 
On the ascent of the plunger, P, in 
the barrel on the working stroke of 
the main rods water flows in through 
the inlet-valve, O, but can only flow 
out slowly through the small cock 
or faucet. A, and will therefore take 
a perceptible time to allow the 
plunger to reach the bottom. The main pump is meanwhile 
at rest. The descent of the plunger, P, either opens the valves 
directly or releases detent mechanism whereby the valves are 
permitted to be opened by another force. 

It will be seen that this arrangement permits the Cornish 
pumping-engine to make a relatively small number of strokes 
per minute with intervals of rest between, or the strokes can be 
made as frequently as with the ordinary rotative mechanism. 
The cataract principle, using a spring instead of the weight of 
the plunger, has been applied to operate the valve mechanism 
of horizontal direct-acting pumps. As such engines are 
double-acting, the graduating-valve will be in a connection 
which joins the two ends of the cataract-cylinder, and the 
plunger is replaced by the piston which fits that cylinder. It 
is obvious that in either case work is stored by the working 
stroke of the main engine and given out as desired after the 
main engine is at rest. 

42. Advantages and Disadvantages of the Cornish 
Pumping-engine. — The primary advantage of the Cornish 
pump is that the motion of the water through the valves and 
pipes is made the controlling element. Large masses of water 



JSNGINES CLASSIFIED BY THEIR USE OF STEAM. 77 

can only be accelerated as demanded by crank motion at the 
expense of considerable work which is unprofitably expended. 
Second, the masses of the pump-rods serve as a reciprocating 
fly-wheel. Third, the single-acting principle of working 
enabled the Cornish pump to work with much greater econ- 
omy than less carefully designed pumping-engines belonging 
to its earlier period. The duty of the best grade of Cornish 
engine stated in the usual form has been about 100,000,000 
pounds of water raised one foot high by the combustion of 100 
pounds of coal. Fourth, its ability to w^ork successfully with 
a very small number of strokes per minute. 

The disadvantages of the Cornish pumping-engine are, 
first, being single-acting it is bulky for a given number of 
foot-pounds of work. The mean pressure in the cylinder 
cannot be high, because at the end of the stroke all living force 
of the reciprocating parts must have been given out. Second, 
having no crank to limit the stroke of the piston, there is the 
danger from overstroke either up or down. If from any 
cause the pump-barrel fails to fill with water, the massive rods 
descend unchecked, and their living force under these circum- 
stances will wreck the engine. Third, the bulk of the cylinder 
and the masses attached to the piston compel an expensive 
and massive foundation greatly in excess of that required by 
an engine of a different type to do the same work. Fourth, 
the intermittent action of the cylinder compels very careful 
provision to keep it warm between strokes, and in spite of all 
care condensation will be considerable. 

43. Single-acting Rotative Engines. — The demand for 
an engine of high rotative speed for electric-light and power 
service which shall be able to be cheaply built with respect to 
fitting, alignment and wear has attracted engine-builders to 
the single-acting principle. In this type, and particularly with 
an inverted cylinder and trunk-engine mechanism with the 
energy of the steam acting with gravity downwards upon the 
upper side of the piston, it is brought about that the effort of 
the steam through the mechanism is in one direction only. 
Hence silent running is secured at high rotative speed because 



78 



MECHANICAL ENGINEERING OF POWER PLANTS. 



the strain on the crank-pin is never reversed, which will be 
the occasion for knock or pound in a double-acting engine 
upon passing the centres,, unless the adjustment and fitting 
are very perfect and the adjustment of the valve-mechanism 
just right. The danger of overheating bearings is lessened 
when the adjustment of fits is of less moment, and it further- 
more becomes a matter of less risk to make use of high initial 




Fig. 63. 

steam-pressure in the cylinders. Continuous action is secured 
by putting two cylinders to act upon the same crank-shaft. 
The two best-known single-acting engines of the rotative type 
are the Westinghouse and the Willans. Fig. 63 shows a 
longitudinal section and Fig. 64 a transverse section of the 
Westinghouse standard engine, and Fig. 65 a section through 
the Willans cylinders. The trunk-mechanism is clearly mani- 
fest in both designs, and the principle which they both repre- 



ENGINES CLASSIFIED BY THEIR USE OF STEAM 79 

sent of securing self-lubrication by having the crank-shaft 
revolve in a closed casing which is filled with water on the 
surface of which floats lubricating oil. The use of pistons of 
different diameters is very convenient in engines of this type, 
and will receive discussion in the sequel. These engines may 
have rotative speeds between 250 and 500 revolutions per 




Fig. 64. 

minute without difficulty, and have been quite a little used 
where it was desirable to couple the armature of electric 
dynamos directly to the engine-shaft. The Willans engine- 
section shows the characteristic central valve within the hollow 
piston-rod. 

44. Expansive and Non-expansive Working of Engines. 
— The third subdivision of engines under the classification now 
being examined is the division of engines into two classes, 



80 MECHANICAL ENGINEERING OF POWER PLANTS, 

according to the manner in which they utilize the elastic 
tension of steam which is given to it by heat. If the length 




fi 



Fig. 65. 



of the rectangle shown in Fig. 66 represent the stroke of the 
piston in a cylinder on any convenient scale of feet, and the 



ENGINES CLASSIFIED BY THEIR USE OF STEAM. 



8i 



height of the rectangle represent on any convenient scale the 
pressure in pounds per square inch due to the elastic tension 
of the steam working in that cylinder, it will be at once 
apparent that the area of that rectangle, being the product of 
the base multiplied by the height, will be the foot-pounds 
exerted on each square inch of that cylinder in that stroke. 
As thus represented, the steam from the boiler passed into the 
cylinder during the entire stroke at the constant pressure 
prevailing in the boiler, and the volume which that steam 




Fig. 66. 

occupied in the boiler has been replaced by the vaporization 
of an equal weight of water to supply its place. The effort 
of the steam is the same at all points of the stroke, and at 
the end of the stroke, when the piston is to reverse, this 
steam must be allowed to escape as exhaust-steam with the 
pressure at the beginning of such exhaust equal to the pres- 
sure in the boiler, and carrying with it as many units of heat 
as are represented by the weight of that steam in pounds 
multiplied by the degrees of heat required to heat the water 
to the point at which it began to make steam, and then to 
make that weight of water into steam at that pressure. Such 
an engine is said to work without expansion, or non-expan- 
sively. It represents the conditions under which the great 
majority of single-cylinder direct-acting pumps work, and a 
good many elevator engines. 

The diagram Fig. 67 shows the pressure upon the piston 
of a typical engine of the other class working its steam 



82 MECHANICAL ENGINEERING OF POWER PLANTS, 

expansively within the cylinder. If the length of the bottom 
line of the diagram represent the length of the stroke in feet 
to any convenient scale, and the vertical ordinates the pressure 
on each square inch of the piston at a similar convenient scale, 
it will appear that the steam flowed into the cylinder from the 
boiler from the beginning of the stroke until the piston had 
moved through a distance represented by the short upper line, 
and that at this point the pressure began to fall, and fell con- 
tinuously until the end of the stroke was reached. The 
pressure at the end of the stroke is represented by as many 




Fig. 67. 

pounds to the square inch as there are units of the pounds 
scale in the vertical height at the end of the diagram. 

The drop of pressure at the point on the upper line where 
the curve begins was caused by the closure of the valve 
admitting steam to the cylinder. This closure is called ** cut- 
off " of the steam, and the volume of steam admitted to the 
cylinder during the part of the stroke represented by the 
straight upper line was expanding without admission of fresh 
steam from the boiler during the rest of the stroke, doing 
work upon the piston, and losing both its pressure and its heat 
in such expansion and work. The evaluation of these changes 
belongs to the science of thermodynamics, but for the present 
purpose it is apparent that the force upon the piston was 
growing less and less from cut-off to the end, but also the heat 
to be rejected by the engine at exhaust and the energy still 



ENGINES CLASSIFIED BY THEIR USE OF STEAM. 83 

resident in the steam are both much less than in the non- 
expansive diagram, such as illustrated in Fig. 66. In engines 
with fly-wheel the living force stored in its mass during the 
first part of the stroke can always be made to compensate 
for the diminishing energy from expansive working, although 
a slightly larger cylinder-volume is required than when work- 
ing non-expansive. The great gain in expansive working 
irom diminishing the amount of heat rejected at exhaust has 
made the expansive method of working practically universal 
^vhere circumstances admit. 

Another method of stating this principle may be used. 
Referring to par. 3, in which each unit of heat corresponds 
to 778 foot-pounds of work, the weight of steam Q entering 
the cylinder during that part of the stroke represented by 
the straight npper line and having the temperature due to its 
pressure represented by T^ will be able to do an amount of 
work in foot-pounds represented by the product QT^Y. 778. 
At the end of the stroke, the same weight of steam Q escapes 
from the cylinder at the reduced pressure, whose temperature 
ivill be represented by T,^. The potential energy in foot- 
pounds represented by that steam at that temperature is 
therefore rejected, and hence the work which has been done 
«pon the piston will be given by the equation 

w^{QT,^^^-{QT,^^z). 

The efficiency of any device or appliance is the fraction whose 
numerator is the work actually done, and whose denominator 
is the work supplied or theoretically to be expected of it. 
The efficiency, therefore, of the steam in the engine-cylinder 
Avill be an equation of the following form : 

^. . g^:778- Qr,778 

The second member of this equation can be simplified by 
dividing all terms by Q . 778, which are factors common to 



84 MECHANICAL ENGINEERING OF POWER PLANTS. 

them all, so that the equation for the efficiency can be sinri- 
plified into the form 

T^ — 7; 
Efficiency = ' . 

From this it appears that the efficiency of the fluid used 
becomes greater as the difference between the initial and final 
temperatures or the pressures belonging to such temperatures 
becomes greater; and furthermore can only become unity 
when the final temperature is the value which belongs to an 
absolute absence of heat-motion of its particles — a condition 
which is not realizable in practice. 

The only objection to expansive working appears when it 
is carried a little further than is wise in one cylinder. In this 
case the walls of the metal cylinder are cooled with the cool- 
ing of the steam within it to a point below the temperature 
belonging to the entering steam. The consequence is that on 
the beginning of the following stroke the hot steam has to 
heat up the metal of the cylinder to its temperature before 
it can produce pressure. Some of it is condensed itself in this 
process of heating the metal, and either becomes incapable of 
doing work or else is re-evaporated into steam during the 
reduction of pressure at the expansion period and cooling the 
cylinder and the steam by the abstraction of the heat re~ 
quired to vaporize it. In the first case more steam is used 
per horse-power than is accounted for by the volume of steam 
apparently present per stroke, and in the second case the 
cooling of the metal of the cylinder aggravates the loss at the 
initial condensation. This phenomenon is called *' internal 
condensation and re-evaporation in the cylinder." It occurs 
even in non-expansive working, and is not to be altogether 
avoided. It imposes, however, a limit to carrying the expan- 
sive principle too far. 



CHAPTER IV. 
CONDENSING AND NON-CONDENSING ENGINES. 

45. Introductory. — In the diagrams shown in Figs. 66 
and 67 the lower line or base-line from which pressure will be 
measured is the line of atmospheric pressure. This, how- 
ever, is not the line of no pressure, inasmuch as the pressure 
corresponding to the one atmosphere at sea-level is the pres- 
sure of 14.7 pounds on each square inch of area. The line of 
perfect vacuum on the exhaust side of a piston should there- 
f(»re be drawn at a distance below the atmospheric line equal 
to 14.7 units of the scale of pressure. 

It is entirely possible so to arrange the working of the 
steam that, after having done its work in the cylinder, instead 
of escaping into the atmosphere at a pressure of 14.7 pounds 
above vacuum it shall escape into a vessel or reservoir within 
Vnich that vacuum is maintained. Since by far the most 
convenient method to secure a vacuum is to condense the 
steam which fills a given volume back into the condition of 
water, engines operating on this principle of exhausting into 
a vacuum have been called condensing engines. Where the 
steam escapes or exhausts from the cylinder into the atmos- 
phere the pressure in the cylinder never falls quite to the 
pressure in the atmosphere, when there is any friction due to 
bends in the exhaust-pipe and other resistances. The steam 
of course ultimately condenses back to water in the atmos- 
phere, but it does not do so in connection with the engine 
itself. Engines exhausting at or above atmospheric pressure 
are called non-condensing engines, and the full-line diagram. 
Fig. 68, when compared with the dotted-line diagram will 

85 



86 MECHANICAL ENGINEERING OF POWER PLANTS. 



show the difference in the action of the steam doing equal 
work in the two cases. The lower Hne in the two diagrams^ 
Fig. 68, represents the pressure on the piston on the return 
stroke, which may be called the back-pressure. The dotted 
line represents the pressure just above atmosphere, while the 
full line diagram shows a pressure of 14.7 lbs. below it. 

The physical principle on which the condensation of steam 
causes the practical vacuum is that one cubic inch of water 
will form 1700 cubic inches of steam at the pressure of one 
atmosphere. If these 1700 cubic inches of steam are cooled 
back to water, they undergo a reduction of volume in the same 

J/5 



40 lbs. Spring 




Fig. 68. 



proportion less only the volume filled by the tenuous vapor 
which even cool water gives off in a vacuum. It will only be 
necessary to draw off the condensed steam by proper appa- 
ratus to enable the vacuum to be maintained which the con- 
densation has created. 

The earliest historic steam-engines of the modern period 
were all condensing engines. Steam at a comparatively low 
pressure above the atmosphere was admitted to the cylinder 
for the working stroke, and upon being condensed the absence 
of pressure represented by the vacuum upon the working side 
of the piston was the principal dependence for the power of 



CONDENSING AND NON-CONDENSING ENGINES. 8/ 

the stroke. Such engines were called low-pressure engines. 
When the engine did not condense so that the back-pressure 
line in Fig. 68 was at atmospheric pressure or above it, it was 
necessary that the pressure of the steam in the boiler should 
be correspondingly raised. Such non-condensing engines were 
therefore run at relatively high pressure, and were called high- 
pressure engines. At one time, therefore, high pressure was 
synonymous with non-condensing, and low pressure synony- 
mous with condensing. This is no longer the case, since nearly 
all condensing engines of modern construction operate with 
steam at high pressure. 

46. Advantages of the Condensing Engine. — The prin- 
ciple of exhausting the steam from the cylinder into a vacuum 
or at a pressure below the atmosphere offers the following 
advantages : 

1. With a cylinder of given area, stroke, and piston-speed 
the net effective pressure is greater than in non-condensing 
engines. This is apparent by comparing the area below the 
atmospheric line in Fig. 68 with the absence of area below 
the atmospheric line in the dotted card in that figure. The 
area below the atmospheric line represents a work in foot- 
pounds done in the condensing engine which cannot be done 
in the non-condensing engine. Furthermore, the expulsion 
of the steam from the cylinder requires the expenditure of 
some work, whereas in the condensing engine the exhaust 
expands into the vacuum-chamber with great rapidity and 
removes back-pressure at once from the piston. The conse- 
quence of this lowered back-pressure and the work below the 
atmospheric line is that the engine delivers more power for a 
given size than the non-condensing engine. In other words, 
the' value for /^ in the horse-power formula has been increased, 
while the other factors remain the same. 

2. The other way of stating this same advantage is that 
the same power will be secured by a smaller cylinder with the 
condensing cylinder than with the non-condensing with the 
attendant advantages of diminished bulk. 

3. The area of the diagram Fig. 68 will be proportional 



88 MECHANICAL ENGINEERING OF POWER PLANTS. 

to the foot-pounds of work done in a stroke. By increasing 
the height of the diagram, as done in the full line of Fig. 68, 
as compared with the dotted line, the same area is secured by 
diminishing the mean length. As the length of the bottom 
line is fixed by its relation to the length of the cylinder, there 
will be secured the same work in foot-pounds when the length 
from the right of the diagram is shortened. The length of the 
upper line denotes the volume of steam admitted from the 
boiler before the admission is cut off by the closure of the 
valve. By shortening this admission a less volume of steam 
is drawn from the boiler per stroke, and consequently less 
water need be supplied and vaporized and consequently less 
coal need be burned. In other words, the condensing engine 
requires both in theory and in practice a less amount of coal 
per horse-power per hour. 

4. Since the pressure in the cylinder varies practically in- 
versely as the volume, it follows that a given volume of steam 
admitted up to the point of cut-off will expand to a lower final 
pressure and still keep up a positive effort upon the cylinder 
in the condensing engine, as compared with the non-condens- 
ing. The consequence of this is that when the stearn is 
rejected from the cylinder at the end of the stroke of the 
piston in the condensing engine, less heat is rejected than 
where such steam escapes at a temperature represented by a 
pressure above the atmosphere. In other words, the condens- 
ing engine utilizes the heat imparted to the steam by the fuel 
more perfectly than the non-condensing engine does. 

5. This latter development is from the gain discussed in 
par. 44. The efficiency was there shown to increase when the 
temperature of rejection is lowered. In condensing engines 
using water for condensation in great volumes it should be 
practicable to bring the final temperature of the steam down 
to that of the usual temperature of natural water, or in the 
neighborhood of 60 degrees Fahr. Inasmuch as it is incon- 
venient to use great volumes of water, engineers are usually 
satisfied to bring the temperature down to ioo°-i30° Fahr., 
which is the temperature corresponding to 7^^ in the efficiency 



CONDENSING AND NON-CONDENSING ENGINES. 89 

formula. In the non-condensing engine T^ will be 212° or 
over. Hence the efficiency in this technical sense is greater 
in the condensing engine than in the non-condensing engine. 

6. The condensation of the steam to the temperature of 
ioo°-i30° gives a quantity of warmed water at hand which 
can be used to pump into the boiler to replace what is turned 
out in the form of steam. This water is heated by heat which 
in the non-condensing engine is rejected or wasted into the air. 
It is an advantage of the condensing engine that it preheats 
the water to be fed to the boiler. This saves fuel and is of 
advantage to the boiler. 

47. Disadvantages of the Condensing Engine — The 
disadvantages of the cond'ensing engine are partly inherent 
and partly accidental or dependent upon the method used in 
applying the general principle of condensation The inherent 
difficulties are as follows: 

1. The lowering of the final temperature and pressure of 
the steam lowers the final temperature of the metal of the 
cylinder. The effect of this cooling of the metal is to increase 
the amount of condensation to be expected within the cylinder 
(see par. 44), and thereby materially to diminish the economy 
which theory would indicate for the condensing engine. The 
diagrams of Fig. 68 give little or no intimation of the steam 
used in heating the cylinder, but the coal used to make this 
steam has to be burned and paid for. The wide range of press- 
ure between the beginning and the end of the stroke causes the 
condensation of steam in the doing of work, and the vaporiza- 
tion of this steam cools the cylinder. The diminished range 
in the non-condensing engine diminishes the losses from this 
cause. 

2. The condensing engine must maintain the vacuum 
created by condensation, by withdrawing the condensed water 
from the vessel or chamber into which the exhaust passes. 
The maintaining of this vacuum imposes a work upon the 
engine itself, or upon a separate appliance, which is not 
demanded by the non-condensing engine. This work is 
caused by the friction of the water and the work of displacing 



90 MECHANICAL ENGINEERING OF POWER PLANTS. 

a given weight of it, and by the friction of the pumps or other 
appliances used. Ordinarily, also, the water used to cool the 
steam must be handled at the expense of the power of the 
engine. If the condensation can be done by natural falling 
water, this difficulty does not hold. 

3. The exhaust from the cylinder carries with it the oil or 
other lubricating material carried into the cylinder for lubri- 
cating the piston, valves and the like. The lubricating 
material must undergo the cooling of the condensing process, 
and gradually fouls and stops up the passages through which 
it passes, or else it goes through to be pumped back with the 
warmed water into the boiler. This presence of lubricating 
oil in boilers is a serious annoyance, inasmuch as a coating of 
such material on heating surfaces prevents intimate contact of 
water with the metal, and frequently causes the latter to 
become overheated and so softened as to be easily forced out 
of shape by the pressure in the boiler. Great care has to be 
taken to separate the oil from the condensed steam in the 
condensing engine to prevent this difficulty. 

4. The condensing engine can only be used where an 
available quantity of water for condensation can be procured 
without excessive cost. This limits the application of the 
principle to stationary practice on land, but is a reason for the 
abundant and extensive use of the condensing engine for 
marine purposes. Condensation by air requires an enormous 
bulk for the condensing appliances, and where water is costly 
or scarce special provision must be made for using the same 
water over and over again. It is practically impossible to 
operate the locomotive as a condensing engine. 

The accidental objections to the condensing engine are those 
dependent upon the methods used for applying the principle. 

1. If the condensing apparatus is driven from the mech- 
anism of the engine itself, the handling of water precludes 
the use of a high rotative speed in such engines. The engine 
cannot be run faster than consistent with the proper working 
of the pumps attached to it, 

2. If the condensing engine operates its own condensing 



CONDENSING AND NON-CONDENSING ENGINES. 9 1 

appliances at comparatively low speeds, the weight and bulk 
for such appliances become inconvenient. 

48. The Condenser of a Condensing Engine — To trans- 
form a non-condensing engine into a condensing one, the first 
addition to be made is the chamber or reservoir in which the 
vacuum, more or less complete, is to be maintained, and into 
which the exhaust-steam is to pass from the cylinder. This 
must be an air-tight vessel, and is called the condenser. It 
may be placed close to the cylinder, or at a moderate distance 
from it if this is more convenient. Its volume relatively to 
the cylinder-volume will depend somewhat upon the appliances 
for exhausting it, but it is rarely larger than one half the 
cylinder-volume in any case. 

The condensation of steam in the condenser is effected in 
one of two ways. The exhaust-steam either meets the water 
which is to condense it in direct contact, or the steam meets 
metallic surfaces which are kept cool by the circulation of the 
cool water in contact with them. In the first case the con- 
densed steam and condensing water meet and mingle. The 
condenser is a plain closed box, and the cooling water enters 
it in a jet. Such direct condensers are often called jet con- 
densers for this reason, and the water of condensation injected 
into the steam directly is known as the injection-water, or 
simply the injection. This term will be used hereafter for the 
water used to condense the steam by any means. When the 
steam is condensed by contact with cool surfaces, which are 
kept cool by the injection, the condensation is called indirect, 
and the condenser is called the surface condenser. The cool- 
ing surface is usually a surface of pipes or tubes made of 
brass or copper to secure rapid transfer of heat, and very often 
coated with tin on both sides to prevent corrosion and galvanic 
action. In frequent marine practice these tubes are made one- 
half inch in diameter. Fig. 69 shows the usual arrangement 
of the direct or jet condenser as used in river-boat practice 
where the injection comes from the water outside of the hull. 
It will be seen that the steam escaping from the cylinder 
enters the condenser at the side and near the top below a 



92 MECHANICAL ENGINEERING OF POWER PLANTS. 

partition which runs across the condenser. This partition is 
perforated with a great number of holes about one-half inch 
in diameter. The pipe entering the side of the condenser and 
working upward through the perforated partition is the injec- 
tion-pipe, which comes from a suitable opening in the hull 
through the skin of the vessel. The injection-pipe has a valve 
in it, operated by a lever or by a hand-wheel (see Fig. 30), 
whereby the flow of injection-water can be cut off and con- 



1 



E 



^ 



I I II II I I I I :i I I I I TSL 



lull \ \ \\^ \ \\ \ iii i i ri i II i i'p y f 



i 




l-^nd 



Fig. 69. 

trolled. It will be apparent that if there is a vacuum in the 
condenser; and the opening of the injection-pipe is below the 
surface of the water outside of the hull, atmospheric pressure 
will force the injection into the condenser with considerable 
energy, so that the injection-valve is usually only partly open. 
In such river-boat engines as are presented in Fig. 30 there 
are usually three entrances to the injection-pipe. The usual 
one used will be the bottom inlet, opening through the hull 
near the keel and of course always under water. The second 
one will be the side inlet, which will be used only when such 
shallow water is to be feared that there would oe danger that 
the bottom inlet would draw in mud or become stopped with 
solid matter. The third inlet will be from the bilge of the 
boat, and will be called the bilge-injection. It will be used 



CONDENSING AND NON-CONDENSING ENGINES. 



93 



only when from a leak or an accident an excess of water has 
come within the skin of the vessel, so that the propelling 
engine can be used to empty the bilges and lighten the duty 
of the bilge-pumps proper. It will be seen that the injection 
descends across the exhaust-steam in a finely divided shower, 
whereby the least weight of water need be used. Sometimes 
the injection is sprayed into the steam through a simple 
nozzle like the rose-nozzle of a flower watering-pot. (Fig. y^^.) 



Fig. 



'O shows the usual arrangement of the surface con- 





FiG. 70. 

denser. There is often no cogent reason other than conven- 
ience determining the question whether the injection-water 
should circulate within the battery of pipes while the steam 
is on the outside, or whether this plan should be reversed. 
English naval practice adopts the latter. It is most usual in 
the merchant marine to have the steam on the outside, 
because less difficulty is met from the clogging of the con- 
densing surfaces by the condensation of the lubricating 
material on the cool surfaces of the condenser, and it is easier 
to clean the outside of the tubes than the inside, and the 
tubes can be drawn through the tube-plate more easily for 
cleansing. The scale from sea-water used in circulation is 
removable without taking out the tube; tubes can stand 
internal pressure better than external; the water circulates 
better; a large surface meets the steam; the design is simple 
and compact; and a packing can be used which contains 
organic matter. For the English plan it may be said that 



94 MECHANICAL ENGINEERING OF POWER PLANTS. 

most of the lubricant is caught at the first tube-plate; the flat 
surfaces of the condenser have only upon them the light 
pressure of the water in circulation, and not the larger press- 
ure of the atmosphere against the absence of pressure within; 
the metal of the condenser radiates less heat in the engine- 
room. On the other hand, packing of the tube-joints must 
be done by some device which will not be affected by the 
steam. The steam enters the surface condenser usually at 




Fig. 71. 

the top, and the cold injection-water enters it at the bottom 
and as it becomes warm in cooling the tubes it is forced 
upwards so as to meet the hottest steam when it is itself 
warmest. This plan of having the injection travel against the 
steam secures the greatest difference of temperatures in all 
parts of the condenser as a whole, and transfer of heat is most 
rapid with greatest difference of temperature between the 
body to be cooled and the absorbent material. The condensed 
steam gathers in the bottom. Fig. 71 shows a form of a sur- 
face condenser designed to avoid one or two main difficulties 
of surface condensers. By reason of the conditions to which 
they are exposed the tubes are subject to changes of tempera- 



CONDENSING AND NON-CONDENSING ENGINES. 95 

ture which cause them to expand and contract, and makes it 
difficult to keep the tubes tight where they enter the two 
heads shown in the previous sketch. This has been sought 
in the prevalent designs by making an expanded or fixed 
joint at one end, and at the other fixing a species of stuffing- 
box kept tight with compressible packing and permitting the 
tube to slide. 

Fig. 72 presents a grouping of such methods of flexible 
joints. 

A is Howden's wick or hemp joint. 

B and C are Lighthall's, packed with papier-mach6. 

D is Winton's hard-rubber ring. 

E is Spencer's rubber washers. 

i^ is Marshall's moulded rubber joint. 

G is Stimer's tube. 

H is Hall's stuffing-box. 

/ is Chapman's joint with Babbitt-metal calking. 

y is a rubber washer with lock-nut. 

K is Sewell's joint, compressing rubber by a cover-plate 
gland. 

L is Archbold's, with brazed brass wire to prevent creeping. 

M is Wilson's, similar to K except that each tube is 
packed separately. 

N is Horatio Allen's soft wood packing. 

Q is Todd's method. 

The joints from A to / do not permit the removal of the 
tube without having to be themselves renewed. The cover- 
plate plan K packs all tubes at once. 

The Wheeler condenser, shown in Fig. 71 and in detail at 
Pin Fig. 72, secures the tube tight in one end only by screw- 
ing, and the circulating water, instead of passing through the 
tube completely, is made to flow through the closed tubes by 
means of the smaller inner tube which is not attached directly 
to the outer. . The difficulty from the tube-joints was a very 
serious obstacle to their first introduction on sea-going vessels. 
Their use now is universal, since this difficulty has been over- 
come. 



9^ MECHANICAL ENGINEERING OE POWER PLANTS. 




CONDENSING AND NON-CONDENSING ENGINES. 9/ 

49. Jet and Surface Condensers — It will be observed 
that the jet condenser acting directly upon the steam with 
the injection will make a given lowering of the temperature 
of the exhaust-steam with less weight of water and with less 
bulk and weight of condenser. From twenty to thirty times 
the weight of steam to be condensed must be used as injection 
in cool seasons or climates, and from thirty to thirty-five times 
with warmer water. On the other hand, if "-.he condensed 
steam is to be pumped back into the boiler the injection-water 
goes with it, and consequently the injection must be pure 
water and not objectionable for use in boilers. 

The surface condenser, while more heavy and bulky to 
handle and cool d given weight of steam discharged as exhaust, 
can be used with any water whatever as to quality. The 
condensed steam leaves the surface condenser as distilled 
water with no impurities in it except the lubricating oil, and is 
therefore a most excellent material to pump back into the 
boiler if the oil can be extracted from it. The surface con- 
denser has for this reason occupied the field with vessels 
traversing salt water, and has furthermore a wide scope on land 
in places where the available water contains solid matter or 
salts or acids which would be injurious to boilers. The same 
water is used over and over again, and the only addition of 
bad water which has to be made to that which filled the 
boilers in the first place is that which is lost by leakage at 
safety-valves, whistles, and joints. The steam-circuit is prac- 
tically a closed one. The surface condenser for sea-vessels 
adds from ten to eighteen per cent to the first cost of the 
engines, but is more economical of fuel for them than jet con- 
densers would be. 

50. The Cold-well. — In stationary practice on land the 
water for condensation and the injection must be supplied from 
a reservoir. In cities having a water-supply the city water 
can be used for this purpose, but ordinarily the quantity 
needed for a plant of considerable size will compel the engineer 
to consider other means. In the older designs it was very 
common to immerse the condenser in the tank from which the 



98 MECHANICAL ENGINEERING OF POWER PLANTS. 

injection was to be drawn. Fig. 73 ; and even where city sup- 
plies under pressure are to be had, it is preferred not to 
connect the condenser to the mains, but to take the injection 
from a tank in which the supply of pressure-water shall be 
controlled by float-valves or ball-cocks. The expense of city 
water has compelled many proprietors to sink artesian or 
other private wells for the purpose of controlling the necessary 
quantity of injection-water, but even this is expensive and 




Fig. 73. 

not always practicable. The tank from which the injection is 
taken was called by the early designers the cold-well, and 
latterly considerable pains have been taken to mak€ it possible 
to use the same injection-water over and over again without 
making the cold-well of unmanageable size. 

Two creneral methods have been followed in the solutions 

o 

which have been sought for this problem. The first has been 
to construct a series of shallow troughs in which the warm 
injection- water flowed in the open air exposed to the action 
of the natural winds. These troughs were arranged one over 
the other with a slight grade, so that the water flowed zigzag 



CONDENSING AND NON-CONDENSING ENGINES. 99 

fashion from the top to the bottom, and after leaving the 
lower end of the latter flowed back to the well. The pro- 
longed exposure in thin films to the vaporizing action of the 
open air and the cooling caused by such vaporization resulted 
in a considerable lowering of the temperature of the injection. 
The other plan, of modern introduction, is to cause the injec- 
tion to descend in a closed tower in a fine state of division 
over tile or wire gauze arranged upon gratings or trays. A 
current of air forced by a fan causes a vaporization of the 
film of warm water pouring over the tile-surfaces, and the air- 
cooling and vaporization combined withdraws the heat from 
the injection, so that as it falls into the cold-well at the 
bottom of the tower it is in condition to be used again. This 
appliance has been in successful operation for some years, and 
is warranted wherever the cost of condensing water per annum 
without such device would exceed the interest upon the cost 
of the plant and the expense connected with operating it. 
Pig. 74 illustrates this arrangement. 

51. The Air-pump and Foot-valve. — The vacuum created 
by condensing the steam by the injection must be maintained 
in the cnodenser. The condensed steam and injection would 
rapidly fill the volume of the condenser if no means were taken 
to empty it. Furthermore, all natural water and the steam 
contain a certain quantity of air which undergoes no conden- 
sation or reduction of volume, and whose presence in the con- 
denser would soon destroy the vacuum created by condensa- 
tion. Some means must therefore be provided to draw from 
the condenser the condensed steam, the injection, and the air. 

There are many different methods for accomplishing this 
result. Referring to the typical river-boat engine. Fig. 30, it 
will appear that attached to the bottom of the condenser and 
driven from the beam of the engine is a lifting-pump having 
a valve in its piston or bucket. This pump is called the air- 
pump, and the plan of driving it from the beam or cross-head 
of the engine is a method which has been very generally fol- 
lowed in all earlier designs. It will be called the method with 
attached air-pump. 



100 MECHANICAL ENGINEERING OF POWER PLANTS, 




SUCTION TANJ^ 



Fig. 74. 



CONDENSING AND NON-CONDENSING ENGINES. lOI 

The air-pump must be a lifting or sucking piston-pump. 
It must meet the difficult condition of withdrawing water and 
air from a vessel within which the pressure is less than the 
atmosphere, and therefore atmospheric pressure cannot be 
counted on to fill its barrel as is the case with the ordinary lift- 
ing-pump. If the piston in the air-pump in Fig. 30 be 
supposed to be rising in its barrel, and the bottom of that 
barrel opens into the condenser through the valve which sep- 
arates them, it will be apparent that as long as the pressure 
in the air-pump is greater than the pressure prevailing in the 
condenser the valve cannot open. The rise of the air-pump 
piston must create below it a rarefaction or vacuum greater 
than that in the condenser before the valve will open and any 
equalization of pressure occur. Furthermore, the water in the 
bottom of the condenser will only flow through the foot-valve 
of the pump by gravity, unless there is enough of it to seal the 
connection between the two volumes, and will then only rise in 
the air-pump sufficiently to counterbalance the differences in 
pressure. The bottom of the air-pump and the foot-valve 
must therefore be below the bottom of the condenser, so that 
the water may fall out of the condenser by gravity. When 
the air-pump reverses and begins to descend, the foot-valve 
closes and remains closed during the descent of the bucket. 
As the bucket goes farther down it strikes the water which 
has flowed from the condenser, and therefore the bucket-valve 
opens by excess of pressure below, and the bucket descends 
through the water to the bottom of its stroke. In its ascent 
the water above the bucket closes the valves and seals the 
piston while the cycle of the first stroke is repeated. 

The foot-valve in most direct-driven engines is a flat 
rubber flap of the necessary thickness (inch to inch and a half) 
which seats upon a grated inclined partition. Access to this 
valve for renewal and repair is had through a bonnet or cap 
formed in the casting just over the grating. The air-pump 
bucket-valves are also usually circular rubber disks, which are 
prevented from rising too far by brass guards. They also 
seat upon grated openings, and are easily accessible from the 



I02 MECHANICAL ENGINEERING OF POWER PLANTS. 



top of the air-pump. From the top of the air-pump the com- 
bined injection and condensed steam are discharged to the 
organ of the condensing engine which is called the hot-welL 

With the surface condenser the air-pump is still required, 
but its function is slightly different. As the injection does 
not meet the condensed steam, the air-pump does not have to 
handle the former, but has only to draw out the condensed 
steam and the air which gets into the condenser with the 
steam and by leakage. The air-pump of the jet condenser is 
usually one eighth of the volume of the cylinder; that is, it is 
of one half the diameter and one half the stroke. In surface- 
condensing engines it is about one twelfth or one thirteenth 
of the cylinder-volume, or perhaps about one half the size for 
jet condensers; it is a single-acting pump in both cases. 

52. The Circulating Pump. — In surface-condensing en- 
gines the handling of the injection through the tubes of the 
condenser is done by a separate water-pump, which is called 
the circulating-pump. In marine practice of sea-going vessels 
the water for injection is taken from overboard through a 
valve in the hull, is forced through the surface condenser and 
then outboard again. The inlet-valve is low down so- as 
always to be below water, even in rough sea, and the outlet- 
valve is usually at or above the normal load water-line. The 
work of the circulating-pump is therefore to overcome the 
friction of the condensing tubes, and to lift the water through 
the few inches of difference of level between the water outside 
and the discharge-level of the overboard-valve. By reason of 
the small resistance and the large volume of water which are 
the conditions of such circulation (seventy times the volume 
of feed-water required by the engine), centrifugal pumps have 
been the very prevalent type of circulating-pumps. They 
are driven by their own independent engines. More recent 
American practice introduces reciprocating-pumps for this kind 
of work with satisfaction (see Figs. 71 and 75). When 
single-acting reciprocating-pumps are used, the volume of the 
cylinder is from one twentieth to one thirtieth of the steam- 
cylinder volume. For small launches where the quantity of 



CONDENSING AND NON-CONDENSING ENGINES. IO3 

steam to be condensed makes such an arrangement practical, 
a form of surface condenser has been used which consists of a 
coil of pipe zigzagging on the outside of the hull on both 
sides of the keel. The steam passes through the inside of 
this coil of pipes, and the motion of the boat causes a con- 
tinual impact of cool water against the coil and produces the 
same phenomena as by the circulating-pump, It has been 




Fig. 75. 

found, as might be expected, that the more rapid the motion 
of the vessel through tlie water the more efficient are such 
condensing coils. The extra . resistance offered by such coils 
is the compensation for the avoiding of the circulating-pump, 
but in small boats it is a distinct gain to get the bulky con- 
denser outside of the hull. 

53. The Independent Air-pump. — The design shown in 
Fig. 30 represents the air-pump driven by the engine-cylinder 
attached by rods to the beam. This may also be secured in 
horizontal engines without beam by driving the air-pump from 
the cross-head as shown in Fig. 16, or from the crank as 



104 MECHANICAL ENGINEERING OF POWER PLANTS. 

shown in Fig. 22. Many advantages follow from abandoning 
the principle of the attached air-pump and driving the air- 
pump independently by a separate steam-cylinder, or in a shop 
by a belt from the shafting. This principle is called that of 
the independent air-pump and offers the following advan- 
tages : 

1. The pump can be located anywhere. The attached 
principle compels the air-pump to work in the plane of the 
main engine if directly attached, and this may make the loca- 
tion for the air-pump either cramped or inaccessible or 
inconvenient. 

2. The air-pump being independent of the main engine 
can be run without it. This is of advantage in starting the 
main engine, since the vacuum in the condenser can be created 
before steam is turned on to the main engine. 

3. The air-pump can be run at varying speeds while the 
main engine is run at a constant speed. This enables the 
designer and runner to provide for varying temperatures of 
the injection-water according to the season of the year, and 
in marine practice according to the latitude and correspond- 
ing temperature of the ocean-water. The air-pump can 
further be run faster than the normal rate in case of leakage 
into the condenser which it may not be convenient to arrest. 
The vacuum will be maintained as it cannot be with the 
attached pump. 

4. Since the air-pump can be run faster, and can usually 
be double-acting, it will be much smaller than the attached 
pump. This is a gain in bulk, a gain in weight, a gain in 
friction, from the lessened weight, and the small-diameter 
cylinder has a less clearance-volume, which is always trouble- 
some when air is to be rarefied. 

5. By detaching the air-pump, which is a water-pump 
as well, the speed of the main engine is not controlled by the 
limitations of satisfactory working of the air-pump. The high 
rotative-speed engine can thus be conveniently condensing. 

The only objection to be urged against the independent 
air-pump is that the small steam-cylinder which drives it uses 



CONDENSING AND NON-CONDENSING ENGINES, IO5 

Steam less economically than the large cylinder of the main 
engine. This is not true when the air-pump is belt-driven. 
The necessary clearance-volume, although smaller in the inde- 
pendent engine, is filled and emptied more often. 

The superior convenience of the independent principle has 
made it a feature of much recent designing. It will be seen 
from Figs. 71 and 75 that it is very simple to combine the air- 
pump and the circulating-pump for surface-condenser practice 
so that one steam-cylinder shall drive both pumps. This 
makes an arrangement which is both convenient and very 
economical of space. 

54. The Gravity Condenser. — It early suggested itself to 
avail of the law that the atmosphere will not balance a column 
of water over 32 feet high. This makes it possible to con- 
struct a condenser which shall require no air-pump. The 
injection and the condensed steam can be thus disposed of, 
but the air in the condenser cannot. The first gravity con- 
denser was proposed by Ransom (Fig. jG)-, his condenser 
consisted of a pot B into whose bottom entered the ex- 
haust-pipe A from the engine, the injection-pipe C, and the 
discharge-pipe O. The injection was carried up through a 
perforated plate towards the top so that the water descended 
in a shower, and the exhaust-pipe A was protected by a 
shield so that water should not fall down into it. The dis- 
charge-pipe was 33 or 34 feet long, and its lower end was 
immersed in the water of the hot-well so that a barometric 
seal was secured, and with highest barometric pressure the 
water would only stand in equilibrium in the discharge-pipe 
at a level below the bottom of the condenser. The small 
pipes, 222 in the diagram, are short lengths within the dis- 
charge-pipe upon which the descending flow of water is to 
act by aspiration so as to induce currents to draw out from 
the condenser by this action the air which gathers in it and 
which lacks a barometric balance. The small pipe H draws 
the heated water for the boiler from the hot-well. 

It will be seen that this gravity or barometric condenser 
dispenses with the air-pump altogether, but requires an injec- 



I06 MECHANICAL ENGINEERING OF POWER PLANTS. 

tion-pump, which is not necessary in the jet condenser 
previously discussed. The lift, however, of such injection- 




FiG. 76. 

pump is comparatively small, and it requires little power to 
run it. The difficulty with the Ransom condenser was the 
trouble from the air. The pot had to be very tight, and the 
aspiration devices were not entirely satisfactory. 

55. The Siphon or Injector Condenser. — Belonging to 
the class of gravity condensers, so far as barometric balance 



I 



CONDENSING .AND NON-CONDENSING ENGINES. 107 




Fig. 77. 



I08 MECHANICAL ENGINEERING OF POWER PLANTS. 

is concerned, but making much more complete use of the 
principle of induced currents for maintaining the vacuum, is the 
Bulkley condenser, shown in Fig. 'j'j . The principle of sealing 




the discharge in the hot-well and locating the condenser at the 
height of 34 feet above the level of the water in such well are 



CONDENSING AND NON-CONDENSING ENGINES. IO9 



retained, but there is no pot as In the Ransom design. From 
the section shown in Fig. 78 it will appear that the exhaust- 
steam receiving a downward direction in passing through the 
gooseneck at the top of the 
apparatus passes through the 
inner cone surrounded by an 
annular cone of water. The 
steam is condensed in this 
conical space, and falls with the 
injection, whose velocity is so 
graded by the cross-section of 
the condenser that air in the in- 
jection is entrained and has no 
opportunity to remain in the 
space where the vacuum is. 
The small vacuum-cone being 
continually created and emp- 
tied prevents the trouble from 
air, which was the difificulty of 
the first form. There is no air- 
pump, but the injection-pump 
is required as before. 

56. The Ejector Condens- 
er with Pump. — There are 
many places where the height 
required for the long leg or 
siphon of the barometric con- 
denser is inconvenient, notably 
at sea. This has given rise to 
a design of condenser (Fig. 79) 
in which the small bulk of the 
injector and its efficient action 
are combined with a pump to 
maintain the vacuum by con- ^^^- 79- 

tinually drawing off the water and air. The exhaust-steam 
enters through the inlet A, and the injection through the inlet 
B. The latter is controlled by an inner pipe C which carries 




no MECHANICAL ENGINEERING OF POWER PLANTS. 




'nil! 



i'nii. 



'1' 



CONDENSING AND NON-CONDENSING ENGINES. 



II 



a deflecting arrangement D\ this throws the injection in a 
finely divided state into the annular exhaust-steam passage, 
and the air-pump below continuously draws off the water 
mixed with air to which a higher velocity is given by reducing 
the cross-section, so that the bubbles of air once caught in the 
water have no chance of rising into the vacuum-space below 
D. Fig. 80 shows a condenser of this form applied to a 
boat-engine. 

57. The Exhaust-steam Ejector Condenser. — It early 
suggested itself to apply the principle of induced currents as 
used in the steam-injector to draw up the injec- 
tion-water and to make use of the living force of 
the water thus set in motion to oppose the balanc- 
ing effect of the pressure of the air. The first a 
design of this sort is identified with the name of 
Morton (Fig. 81) in England, and the more usual 
forms with the name of Schutte in Germany and 
America (Fig. 83). The philosophy of the 
Schutte injector condenser depends on such an 
enlargement of the discharging end of the con- 
denser that when the condensed steam and in- 
jection leave the outlet they have such a veloci- 
ty as just to overbalance the tendency of the 
-water in the hot-well to flow through that outlet back into 
the space where the vacuum due to condensation is main- 
tained. As will appear from the sectional cut (Fig. 82), the 
steam enters through the side into an annular chamber, and 
passes through a series of inclined orifices or nozzles. The 
steam moves with considerable velocity, and draws in water 
from a cold-well A (Fig. 84), and when the steam and water 
meet, the steam is condensed and flows with the rapidly mov- 
ing water out through the discharge into the hot-well B. The 
discharge is sealed as shown in the general view, and the 
velocity of flow overbalances atmospheric pressure on the well. 
The small steam-connection enables water to be drawn into 
the condenser on the injector principle, in order to start it 
when water does not flow naturally to this level. The bypass 




112 MECHANICAL ENGINEERING OF POWER PLANTS. 

controlled by the valve permits the exhaust to be carried ta 
the open air when for any reason it is desirable to run the 
engine non-condensing. 

It will be observed that this arrangement also, like that ia 



outsiolC view. 



6ECTIONAI. CUT 
A 




Fig. 83. 



Fig. 82. 



par. 56, enables the condenser to be operated without the 34. 
feet of elevation. The series of gravity siphon and ejector 
condensers are all jet or direct-contact condensers. 

58. Pump Condensers. — For mining purposes and ia 
cases where the disposing of exhaust-steam is a feature of the 
problem which must be considered, it has been quite usual to- 



CONDENSING AND NON-CONDENSING ENGINES, II3 



turn the exhaust-steam from the driving cylinder into the 
suction-pipe upon which the water end was acting. This has 
been a very prevalent practice in England, and several devices 




for the convenient application of the principle h ive been pro- 
posed. Fig. 85 shows such a condenser in which the propor- 
tion of the suction which is used as condensing water is; 
controlled automatically by the float F. The water from the 
well enters through an opening 5, and the opening D connects 
the condenser to the suction-orifice of the pump. The 



114 MECHANICAL ENGINEERING OF POWER PLANTS. 



exhaust-steam enters at E, with a provision for free discharge 
to the air if for any reason the pump is to be run non-con- 
densing. This principle of course can be appHed in a great- 
variety of ways. 




59. The Hot-well — Where there is an excess of water 
resulting from mixing the injection with the condensed steam 
above that required by the boiler, the air-pump will discharge 
into a hot-well. In engines with surface condensers the hot- 
well becomes a much less significant organ, because only the 



CONDENSING AND NON-CONDENSING ENGINES, II 5 

condensed steam is delivered by the air-pump while the injec- 
tion or cooling water is passing upon another circuit. 

Referring to Fig. 30 as a typical river-boat engine with 
attached air-pump, it will be observed that the top of the air- 
pump, which is the discharging end, is enlarged into a cylinder 
of nearly twice the diameter, fitted with a loose cover. This 
enlargement of the air-pump is the hot-well. In engines 
operating with independent air-pumps the hot-well will be any 
convenient tank or reservoir. It need not be tightly closed, 
as there is no pressure in it, and it simply has to take care of 
warm water and serve as a cistern from which the boiler feed- 
pumps may draw their suction. In land practice it is usually 
arranged with an overflow whereby the excess of water not 
needed by the boilers may escape to waste. In river-boat 
practice the excess is usually taken care of by pumps. 

60, The Feed-pump. — It is usual in typical river-boat 
engines to attach to the rod of the air-pump one or more 
brackets or half cross-heads, whereby the rod from the beam 
shall operate the pump or pumps which take care of the water 
discharged into the hot-well. In Fig. 1 1 this smaller pump 
is operated from the small beam which drives the air-pump. 
In engines of this class these pumps must have capacity suffi- 
cient to empty the hot-well continuously. Where the hot- 
well can overflow as on land, such pump need have only a 
capacity sufficient to feed the boilers with the water which 
they require. In the former case, where the pumps are 
handling an excess of water, it is common to arrange the 
discharge from the pumps to branch into two outlets. One 
of these outlets goes to the boiler, and the other goes over- 
board through the hull. The valve in the overboard branch 
will control the proportion which goes through each branch, 
since if that valve be wide open the entire delivery of the 
pumps must go overboard, because the pressure in the boilers 
must be overcome before the water will flow through the 
branch connected to them. On the other hand, if the valve 
is shut in the overboard branch, the entire discharge of the 
pumps goes into the boilers. At intermediate degrees of 
closure, part will go overboard and part into the boilers. 



CHAPTER V. 

SIMPLE AND CONTINUOUS-EXPANSION ENGINES. 

6l. Introductory. — In the designs and types which have 
preceded, the steam has entered the working cylinder from 
the boiler, and after doing its work, has been exhausted either 
into the atmosphere or into a condenser. It has also been 
shown that it is of advantage to use the steam in such a way 
as to take advantage of the principle of expansive working 
(par. 44). It has further been seen that it is of advantage to 
secure a high pressure in the cylinder if a powerful engine is 
to be obtained without increasing its bulk or weight (par. 35). 




Fig. 90. 

The lower limit of pressure upon the piston is imposed by 

the lowest temperature usual with condensing water (par. 45). 

If thus, with a fixed lower limit, the diagram of Fig. 90 

116 



SIMPLE AND COMPOUND ENGINES. 11)^ 

be constructed so as to have the initial volume of steam 
admitted into the cylinder bear a very small relation to the 
final volume when the stroke is completed (which is the con- 
dition necessary with high expansion and considerable dif- 
ference between 7", and T^), it comes about that the diagram 
of pressure resembles that shown in that figure. 

If in this the length of the upper or admission line repre- 
senting the portion of the stroke during which admission of 
steam from the boiler is taking place be so short as is repre- 
sented, it is apparent that the boiler-pressure does not act 
very long, nor does it act upon the crank at an angle advan- 
tageous to produce rotation. Furthermore, the c^dinder- 
diameter with such high grade of expansion has to become 
large in order to have this diminished mean pressure do the 
work required. The type of engine which is known as the 
compound or multiple-expansion engine is one in which the 
expansion of the steam is continuous in more than one cylin- 
der whose volumes shall be so adjusted to each other that the 
pressure of the steam shall be greatest in the smallest of the 
series. When the expansion is continuous in two cylinders it 
is called a compound engine. When it is continuous in three 
stages, and whether done in three cylinders or four, it is 
called a triple-expansion engine. When the expansion is con- 
tinuous in four stages, whether done in four cylinders, five 
cylinders, or six, it is called a quadruple-, or by the general 
term a multiple-expansion engine. When there are two 
cylinders, the one which receives steam from the boiler is 
called the high-pressure cylinder, and the larger one receiving 
the steam from the high-pressure cylinder and expanding to 
the lower-pressure and exhausting it is called the low-pressure 
cylinder. Abbreviations for these names are H. P. and L. P. 
When there are three stages in the expansion, the middle 
cylinder of the three is called the intermediate cylinder 
(I. P. or M. P.). When there are four stages, the one receiv- 
ing steam from the high-pressure cylinder is called the high- 
pressure intermediate, and that which receives steam from the 
high-pressure intermediate, expanding it and exhausting into 



Il8 MECHANICAL ENGINEERING OF POWER PLANTS. 

the low-pressure cylinder, is called the low-pressure inter- 
mediate. Expansion has not been carried on any practical 
scale farther than four stages. 




62. Action of Steam in Compound Engines. — By a refer- 
ence to Fig. 33 or Fig. 34, which present compound pumping- 
engines, it will be seen that two cylinders of differing diameter 
are connected to the common beam. The steam may be 



SIMPLE AND COMPOUND ENGINES. 1 19 

imagined to enter the smaller cylinder from the boiler, and 
to exert its pressure continuously throughout the said stroke, 
giving such a diagram as is given in Fig. Gd. At the com- 
pletion of the stroke, instead of exhausting to the atmosphere 
or condenser, the exhaust of this smaller cylinder is into the 
bore of the large. The diameter of this larger cylinder is 
twice that of the smaller or nearly so, so that its volume is 
four times that of the smaller. The steam then at the com- 
pletion of the stroke of the larger cylinder will have a volume 
four times that which it had when it left the small cylinder, 
and a pressure approximately one fourth that with which it 
entered the smaller cylinder. In other words, both cylinders 
have operated without cut-off of admission, and yet the 
steam has been expanded four times by reason of the differ- 
ence in volume. If the first or high-pressure cylinder was 
operated with a cut-off of one half or one quarter of its 
stroke, the expansion into the larger volume would hav^e made 
an increase of eight or sixteen times the volume and a terminal 
pressure practically one eighth or one sixteenth, respectively, 
of the initial pressure. 

It will be seen that the pressure which drives the large 
cylinder is a back pressure upon the smaller one, but by the 
difference of area receiving this pressure the effect upon the 
larger cylinder is a positive or working effect. If the cylin- 
ders were of the same diameter, they would simply act as one 
hollow piston. The space between the two pistons would be 
like a hollow space between the faces into which the steam 
escaped after a working stroke before it was exhausted. 

It is to be noted that the diameter of the largest or low- 
pressure cylinder in the series is the one which determines the 
horse-power or capacity of the engine. The high-pressure or 
small cylinder is inserted between the low-pressure cylinder 
and the boiler as the additional cylinder. This is manifest 
from the fact that it is the low-pressure cylinder which is full 
of steam when the exhaust takes place, and is therefore the 
area upon which the average or mean pressure is to be com- 
puted. In the triple- or quadruple-expansion engine the 



120 MECHANICAL ENGINEERING OF POWER PLANTS. 



action of the steam is identical with that in the compound, 
using three or four cyHnders or stages instead of two. 

63. Mechanism of the Compound Engine. — The plan of 




Fig. 91. 

the compound engine with continuous expansion in more than 
one cylinder was first proposed by Hornblower (1781), and was 
patented by Woolf in 1804. The feature of action in these 



SIMPLE AND COMPOUND ENGINES. 



121 



early or Woolf engines was that the pistons were moving 
either in the same direction or in opposite directions in the 
same phase of the crank motion. The Hornblower engines 
had two cyhnders side by side, operating on the same side of 
the centre of the beam, as appears in Fig. 91. The Woolf 
engines were mostly horizontal engines with the two pistons 
on the same continuous piston-rod. If the two pistons were 
attached on opposite sides of the beam as in Fig. 33, they 
would always be moving in opposite directions, but in the same 




Fig. 92. 

phase and reach the end of their stroke at the same time (see 
also Fig. 34). 

When the two pistons are on the same piston-rod the 
engine is called a tandem engine, whether arranged horizontally 
or vertically. It is perhaps a little more usual in horizontal 
engines to put the low-pressure cylinder nearer to the crank, 
because its greater weight comes nearer the centre of gravity 
and the massive part of the bed-plate, Fig. 92. As the work 
is supposed to be equal, there is no reason for adhering to this 
arrangement if it is more convenient to reverse it (Fig. 93). 
The vertical tandem compound is sometimes called the steeple 
engine (Fig. 94), and in this type the low-pressure cylinder is 



122 MECHANICAT, ENGINEERING OF POWER PLANTS, 

always below, and the lighter high-pressure above. In the 
tandem compound, however, in either form the entire work of 
the two cylinders is exerted through the common piston-rod 
upon one crank-pin. 

The great development of the compound engine for marine 
practice involves the advantages of applying the work of the 
two cylinders to separate cranks. These two cranks will 
compel the two cylinders to be located side by side, and whea 
arranged in the plane of the propeller-shaft, as is usual ia 
marine practice, they are called fore-and-aft engines. The 




Fig. 93. 

cranks of such engines with two cylinders are likely to stand 
in one of three relative positions to each other. The first 
and most natural is to have the cranks opposite or 180° apart. 
By this arrangement the two cranks are on opposite sides 
of the shaft, and therefore the weights of the reciprocating 
parts are balanced. This does away with one of the objec- 
tions to the single-cylinder vertical engine (par. 17). Similarly 
the effort of the two cylinders is balanced upon the shaft so 
that less of it comes upon the bearings, particularly those com- 
ponents of the effort of a single cylinder which the bearings 
must endure when the connecting-rod is working at angles 
unfavorable to rotative effect. This arrangement is especially 
favorable for vessels intended for shallow water, as it diminishes 
the tremor caused in a flexible hull by an alternating effort ia 
unbalanced arrangements. This plan also makes the connec-^ 
tion between the cylinders exceedingly simple and directs 



SIMPLE AND COMPOUND ENGINES, 



123 




Fig. 94. 



124 MECHANICAL ENGINEERING OF POWER PLANTS. 

The low-pressure piston is always moving in the direction 
opposite to that of the high, and consequently the exhaust 
from the completed stroke of the high-pressure piston crosses 
straight over to the same end of the low-pressure to drive it 
in the direction opposite to that of the high pressure. This 
is an advantage of the beam arrangements illustrated in Figs. 
33 and 34, which have very short connections, as will be seen. 
A fourth advantage of this arrangement for sea-going vessels 
is that the weight of the reciprocating parts serves as a species 
of fly-wheel to take care in part of excessive energy when the 
screw comes to the surface of the water in heavy seas and 
suddenly relieves the shaft of its proper resistance. 

A second arrangement of fore-and-aft engines with two 
cranks is to have them parallel. This is very little used in 
comparison with the previous arrangement, although offering 
the advantages of distributing work on more than one crank- 
pin. It does not have the advantages of balance offered by 
the preceding plan, nor the advantage of equalizing effort 
offered by the third plan. 

The third arrangement is to place the cranks quartering 
or 90° apart. This plan balances weight in certain parts of 
the revolution only, but equalizes the turning effort upon the 
shaft. One crank is at its best position when the other is 
passing the dead-centre with no rotating leverage, and for 
this reason this is one of the most preferred arrangements for 
stationary use. A difficulty is introduced, however, because 
the high-pressure cylinder is at half-stroke with half the 
cylinder full of steam to dispose of, when the low-pressure 
piston is at its dead-centre with no volume but the clearance 
to receive it. This compels the introduction between the two 
cylinders of a receiver which has a volume of sufificient size 
to receive the exhaust from the high-pressure cylinder, and to 
deliver it to the low without too great pulsation or wide 
variation in the pressure prevailing in it. Adequate receiver- 
volumes are easily secured for engines whose cylinders are 
sufficiently separated in the pipe or passage which connects 
them. In designs for stationary power purposes in which the 



SIMPLE AND COMPOUND ENGINES. 125 

fly-wheel or belt-wheel is placed so as to revolve in the plane 
between the two cylinders so that the steam from the high- 
pressure cylinder has to cross the space left for such fly-wheel, 
the engine has been called a cross-compound (Fig. 95), which 
will serve as typical of this very popular arrangement. It 
will be seen that the equalization of turning effort from the 
quartering cranks will diminish probable weight of fly-wheel 
required to maintain constant motion. 

64. Beam Compounds. — There are comparatively few 
usual arrangements of compound engines operating the beam. 
Two cylinders may take hold upon opposite ends and be 
parallel to each other (Fig. 33) or inclined to each other (Fig. 
32). They may take hold upon the same side of the beam 
(Fig. 91). This last arrangement is historically an early one 
and is identified with the name of McNaught, an engineer 
who increased the economy of many early extravagant engines 
designed for low pressure by adding the small or high-pressure 
cylinder at the side of the original larger cylinder of such 
beam-engine, and increasing the boiler-pressure carried. In 
engineering literature of the last generation this alteration was 
called McNaughting an engine. In certain forms of pumping- 
engines the steam-cylinders have been put above the beam, 
as in the design of Mr. E. D. Leavitt, for the handling of the 
sewage of part of the city of Boston, somewhat as shown also 
in Fig. 34. The advantage of applying the effort on the 
opposite sides of the beam is to diminish the effort upon the 
beam-centres, and derives the same advantages as in the first 
arrangement of the fore-and-aft engines. When the beam is 
triangular, as in some types of pumping-engines, the effect on 
the mechanism, of the steam part is not affected (Fig. 36), nor 
if cylinders inclined to each other operate on a common pin 
(Figs. 22 and 96). 

65. The Diagram of Steam Effort in a Compound 
Engine. — It will be apparent that a diagram which shows the 
pressures on the piston of a high-pressure cylinder of a com- 
pound engine will occupy a position considerably and mainly 
above the line representing atmospheric pressure, inasmuch as 



126 MECHANICAL ENGINEERING OF POWER PLANTS. 

Jill mi (if 




SIMPLE AND COMPOUND ENGINES. 12/ 




128 MECHANICAL ENGINEERING OF POWER PLANTS. 



the exhaust line of the return stroke will be the driving-pres- 
sure for the other or low-pressure cylinder. Furthermore, the 
diagram of pressures upon the low-pressure cylinder should 
have its upper line the complement of the lower line of the 
high-pressure diagram, because the larger piston is being 
driven by the steam which escapes from the smaller cylinder. 
Any discrepancy or lack of harmony between these lines in a 
Woolf engine without receiver indicates losses from friction, 
condensation, or unnecessary expansion in the clearances or 
passages between the two cylinders. In the receiver engine 
the steam in that receiver is to be treated as a steam spring 
receiving and storing work from the high-pressure cylinder 




Fig. 97. 

and giving it out unaltered to the succeeding stroke of the 
low-pressure cylinder. Any discrepancy between the lines of 
the two diagrams for the two cylinders indicates a drop caused 
by free expansion from the high-pressure cylinder into the 
receiver without doing work in driving the low-pressure 
cylinder, as well as the losses from friction and condensation 
present in the other type. Such loss by free expansion is not 
usually recovered, and should be guarded against if the condi- 
tions of operating the engine permit it. 

It is supposed in Figs. 97 and 98 that two such diagrams 
are drawn wath the same vertical scale representing pressures 
per square inch, and the same horizontal scale representing the 
stroke of the engine. It becomes apparent, however, at once 
that, so far as the effort upon the crank-pin is concerned, the 
difference in the diameter of the two cylinders introduces an 
inequality of work which must be compensated. If the rela- 



SIMPLE AND COMPOUND ENGINES. 



129 



tive volume of the two cylinders be as four to one, then the 
area of the high-pressure diagram should be reduced in the 
ratio of four to one. This reduction can be made either by 
reducing the height ordinates or the length units in the propor- 
tion of four to one. As it is convenient to keep the vertical 
scale of pressures constant in order to enable the law of change 
of pressure with change of volume to be observed in the con- 
tinuous expansion, it is preferred to reduce the diagram Fig. 
97 by shortening the length of the upper diagram at each 
selected distance above the atmospheric line in the proportion 
of one to four and thus get a new diagram by points. 

Thus in Fig. 98 the length cd is one fourth the length 




CD in the original diagram. It will thus appear that the 
reduced diagram will now represent on the same scale as the 
low-pressure diagram of Fig. 97 the work delivered upon its 
crank-pin, and we therefore have the net indicated work done 
in the two cylinders presented by the combined diagram 
shown in Fig. 98 at the right hand. This indicates to the 
eye the continuance of the expansion in a compound engine, 
and shows the space for loss between the two cylinders which 
would not be present if the expansion were in one cylinder 
only. It is this area which designers of continuous-expansion 
engines are to reduce, and it is in spite of this loss that the 
compound engine is superior to the single. Care must be 
taken in combining the diagrams of effort of steam in the two 
cylinders to put them in their right relation to each other 
vertically. This is accomplished by means of properly relating 



130 MECHANICAL ENGINEERING OF POWER PLANTS. 

them to a vertical line drawn outside of the actual diagram at 
a distance beyond it which shall represent a volume equal to 







Fig. 90. 




Fig. 99. 
that of the clearances in each cylinder. The diagrams should 
be placed one over the other, so that these lines representing 
a zero clearance volume shall coincide. (Fig. 90.) 



SIMPLE AND COMPOUND ENGINES. I3I 

In a triple- or multiple-expansion engine where the expan- 
sion is in three or more stages, the reduction of the diagram 
of effort is identical in principle. The area of the intermediate 
and high-pressure cylinder diagrams are reduced lengthwise 
by the proportion which each bears to the volume of the low- 
pressure cylinder, and the three or more diagrams are super- 
posed with reference to their lines of clearanee-volume. Fig. 
99 shows such a combined triple-engine diagram. 

66. Arrangement of Cylinders in Multiple-expansion 
Engines. — The triple-expansion engine is most frequently 
arranged with its cylinders fore and aft in vertical engines or 
side by side in horizontal engines, with the three cranks 120° 
apart when but three cylinders are used (Fig. 17).' So far as 
the convenient passage of the steam is concerned, it is usual 
to put the intermediate between the other two. This is the 
most prevalent arrangement in marine practice, and in the ver- 
tical triple-expansion engines usual in electric-light and power 
stations. The convenience of balancing weights symmetrically 
in marine practice has brought about occasional divergencies 
from this natural arrangement in order to bring the heavy and 
bulky low-pressure cylinder nearer to the middle of the engine. 
The same condition of bulk and weight for the large cylinder 
has brought about the plan of adding to the number of 
cylinders, without increasing the number of stages of expan- 
sion. Furthermore, the constructive difficulties of lengthening 
the engine and its crank-shaft to accommodate four cranks, 
and the great advantage offered by the 120° arrangement of 
the triple engine, have induced the designers of quadruple 
engines to get their four stages with not more than three sets 
of cranks. Figs. 105 and 106 show type arrangements in 
elevation and direction of the steam-currents for triple and 
quadruple engines respectively. 

67. Reheaters for Compound Engines. — The study of 
the combined diagram of compound engines early indicated 
that there would be advantage in diminishing the area which 
represents lost work if the steam could b& reheated or regen- 
erated in its way from the high-pressure to the low-pressure 



132 MECHANICAL ENGINEERING OF POWER PLANTS. 





HP. 

1 




r — ' — 


1= 


r 




M 
2 


P. 




L 


^• 


' ■ 'iE 


y >^ 




-% 


g- 





HlP. 




Fig. 105. — Grouping of Cylinders of Triple-expansion Engines. 



SIMPLE AND COMPOUND ENGINES, 



ni 



/ 



p. 



r^ 



M]P. 



L.'P. 

.41 



MLP. 

3 



MlP. 

2| 



^5. 



LP. 

4| 



T 




Fig. io6. — Grouping of Cylinders in Quadruple-expansion Engines. 



134 MECHANICAL ENGINEERING OF POWER PLANTS. 

cylinder. Reheating would supply additional heat to com- 
pensate for that consumed without return in the high-pressure 
cylinder, and would vaporize the water of condensation from 
doing work before the steam entered the second cylinder. It 
is more economical to vaporize such condensed steam by heat 
supplied before expansion begins than to have the vaporiza- 
tion follow the reduction of pressure during expansion in the 
cylinder. In this latter case the heat required for vaporiza- 
tion is withdrawn from the metal of the cylinder, or from the 
working steam, and the latter needs its heat to work with. 

It has, therefore, been a feature of the design of many 
recent successful compound engines to introduce a coil of pipe 
carrying hot steam from the boiler into the receiver between 
the cylinders. The working steam in the receiver passing 
around outside of this coil has its temperature and pressure 
raised, and is dried before passing to its work in the succeed- 
ing cylinder. Fig. 107 illustrates a form of such receiver with 
its heating tubes, and in Fig. 108 is shown the disposition of 
such a reheater in its relation to the two cylinders. It is an 
advantage of the cross-compound arrangement that it is par- 
ticularly favorable both in principle and construction to 
benefit from the introduction of the reheater. Fig. 34 also 
shows a disposition of the reheater in the receiver. 

68. Compounding above the Atmosphere. — In the dis- 
cussion which has preceded it has been assumed that the 
larger or low-pressure cylinder of a compound engine was a 
condensing cylinder, and that the steam after working In 
it escaped into a vacuum chamber. This is not essential, 
but the larger cylinder can exhaust into the air when it is 
not convenient or desired to provide condensing appliances. 
Fig. 109 shows the Westinghouse compound engine con- 
structed to meet this condition, and all the forms of compound 
locomotive are representatives of this class. They offer all 
the advantages of the principle of continuous expansion, and 
avoid whatever is introduced of complication by the require- 
ment to condense the steam. They can be arranged accord- 
ing to any system, and the only disadvantage is that Intro- 



SIMPLE AND COMPOUND ENGINES. 



135 




136 MECHANICAL ENGINEERING OF POWER PLANTS. 




SIMPLE AND COMPOUND ENGINES. 



137 



duced by the larger diameter of the cyhnder when exhaust- 
ing. 

A back pressure of the given intensity acting upon the 
larger area causes a negative work upon the expelling stroke 
greater than when the exhaust is from the smaller cylinder. 
Compounding above the atmosphere is also used with conspic- 
uous effect for medium-sized pumps without fly-wheels, where 




Fig. 109. 

the steam must follow without reduction of pressure through- 
out the entire stroke of the piston. The desired reduction in 
terminal pressure is secured without causing too great varia- 
tion in the driving effort of the steam. 

69. Compound Locomotives. — The arrangement of cylin- 
ders in the compound locomotive working above atmospheric 
pressure is usually met in one of three ways. First, the 
two-cylinder compounds, which are cross-compound engines 
with the reheater in the smoke- box, using waste gases as the 
heating mediumo The cranks are quartering as usual in the 



138 MECHANICAL ENGINEERING OF POWER PLANTS. 

locomotive, and the high-pressure cylinder is on the left side 
and the low-pressure on the right outside the frames in the 
position usual in the American locomotive. In order that 
such an engine may have sufficient starting power, it is usual 
to arrange that when the receiver is empty the opening of the 
throttle-valve admits steam from the boiler to the low-pressure 
cylinder as well as to the-high. This is a necessity, further- 
more, with quartering cranks to meet the case of the high- 
pressure cylinder having its piston at its dead-centre. As the 
receiver fills from the exhaust of the high-pressure cylinder, 
the pressure prevailing in it acts upon a piston which controls 
a valve which has been called the intercepting-valve, and 
when that receiver pressure is sufficient, boiler-steam is 
automatically shut off from the low-pressure cylinder, and 
from that time on the engine works as a compound. 

The second arrangement has three cylinders. This is a 
more prevalent European design, and is not used in America. 
Usually the two cylinders which form the low-pressure stage 
are outside the frames in the position of the usual outside- 
connected engine, and the high-pressure cylinder is between 
the frames under the smoke-box. This central cylinder drives 
the forward driving-wheels by means of a cranked axle, and 
the outside cylinders drive the rear or trailing wheels by out- 
side crank-pins. This arrangement is also sometimes reversed. 

The third arrangement is the four-cylinder compound in 
which the high- and low-pressure cylinders are attached in 
pairs on each side of the engine, in the common cylinder 
location, to a common cross-head, from which the usual driv- 
ing-rod passes to the crank-pins and wheels. 

The advantage of this is that the engine works compound 
exactly as the single engine, and no material modifications of 
valve-gear are required. The high-pressure cylinder is above 
the low, and the two pistons move in the same direction on 
each side. Hence the steam exhausting from one end of the 
high-pressure cylinder has to cross diagonally to the other 
end of the low-pressure. This type requires no receiver and 
permits no reheater. The advantages of the compound 



SIMPLE AND COMPOUND ENGINES. 1 39 

locomotive beyond those which it enjoys in common with any 
compound engine are the result of the lower terminal pressure 
at which the exhaust escapes. This is favorable to economy 
in the fire-box, because the fire is less torn by the pulsation 
of the exhaust, which causes the draught, and in cities the 
diminished noise of the escaping exhaust makes the locomotive 
less of a nuisance. 

70. Advantages of the Compound Engine. — The princi- 
ple of securing expansion by the continuous working of steam 
in cylinders of increasing volume is to be defended by reason 
of the following advantages: 

1. The high grade of expansion and the difference between 
the initial and final temperature in the steam used is secured 
with an admission of steam into the cylinder through a longer 
proportion of the stroke than in the single cylinder. It has 
been seen (par. 44) that the efficiency of the fluid used in- 
creases with the difference in the initial and final temperatures. 
The work of the steam reaches the crank in angles more favor- 
able to produce rotation. 

2. With the terminal temperature at exhaust fixed by the 
temperature possible with the means used to condense the 
steam, the compound principle enables higher pressures to be 
used in the boilers as initial pressures in the cylinder. To 
increase the pressures in the boilers is to carry more stored 
energy in a given space; to use higher pressures is to enable 
each cubic foot or pound of steam to carry more energy into 
the engine-cylinder, and a given quantity of heat raises the 
pressure of steam more rapidly after the steam has become a 
complete gas than it does at lower pressures, when a large 
part of the heat is absorbed in changing the molecular condi- 
tion of the water. 

3. By receiving the high-pressure steam from the boiler 
first upon a cylinder of small area, as in the compound engine, 
the strain upon the mechanism at the joints and moving mem- 
bers is less than if that same pressure had to be received at 
the beginning of a stroke in a cylinder, and against a piston 



140 MECHANICAL ENGINEERING OF POWER PLANTS. 

of a large diameter. Less loss from friction also follows during 
the less effective angles of the stroke. 

4. From the longer period of admission discussed in num- 
ber one above, it follows that a more advantageous arrange- 
ment for admitting and cutting off the steam becomes 
possible. With the single cylinder and early cut-off in it, the 
openings to admit steam would have to be closed so early 
that it would be difficult to admit steam through wide and 
generous ports or passages. Such single-cylinder valve-gear 
with narrow areas for steam would introduce the difficulty 
known as wire-drawing of the steam. This is a phenomenon 
present when the pressure of steam is reduced by compelling 
it to pass through a narrow or constricted opening. 

5. With high-pressure steam it is difficult, both by reason 
of changes of shape due to heat and by reason of the pressure 
itself, to make the valves controlling the admission of steam 
so that they shall be and remain tight. In the compound 
engine the steam which leaks past the valve of the first or 
high-pressure cylinder does not leak to waste into the air or 
condenser, but into a later cylinder in the chain in which, it 
expands and does work. 

6. If by reason of doing work in expanding there is a 
transformation of heat into work which must be compensated 
by a condensation of the steam in the first cylinder, that 
water reheated and expanding at the lower temperature does 
work in the later cylinder of the chain instead of escaping 
unutilized through the exhaust. 

7. In those forms of the compound engine in which the 
work of the several cylinders reaches the crank-shaft, each 
through its own crank-pin, there is the advantage of such dis- 
tribution, for this avoids the concentration for large engines of 
great energy on small areas, and enables designers to avoid 
either excessive lengths or inconvenient diameters for their 
crank-pins. When the crank-pin becomes of inconvenient 
diameter with respect to the length of the crank, the angle 
-during which the pressure of steam is available to produce 
rotation of the crank is diminished. 



SIMPLE AND COMPOUND ENGINES, HI 

8. The turning effort is equalized when the compound 
engine is arranged to have its cranks quartering. This 
diminishes the weight of the fly-wheel. 

9. The compound engine gives an opportunity to improve 
the quality of the steam during the process of expansion 
when it is possible to use a reheater as discussed in par. 6^ . 

10. The clearance-volumes of the small-diameter cylinder 
carry less steam by weight than if the steam had to fill the 
clearance-volume of the large cylinder. The steam in these 
clearance-volumes is also used expansively in the later cylinder, 
instead of being rejected as would be the case in the single 
cylinder. 

11. The hottest steam is used in the cylinder of the 
smallest volume, causing a diminished loss from radiation and 
condensation due to cool external air 

12. The greatest advantage incident to the use of the 
principle of continuous expansion in several cylinders is that 
thereby the range of temperature between the initial and final 
states of each cylinder is less than it would have to be if the 
expansion were in the one cylinder only. The law of transfer 
of heat from one body to another is that the transfer is rapid 
in proportion as the difference in temperature is greater. The 
less the difference of temperature between the incoming and 
outgoing steam in any cylinder, the less condensation occurs 
when the hot steam enters. This is a particularly favorable 
condition for the large and low-pressure cylinder, whose^ ends 
are alternately open to the comparatively low temperature of 
steam as it is escaping into the condenser. It is of great 
advantage that the high-temperature steam fresh from the 
boiler should not have to meet the relatively cool metal and 
large surface of this low-pressure cylinder. 

71. Disadvantages of the Compound Engine — When it 
is recalled that the low-pressure cylinder is the fundamental 
unit, and determines the working capacity of the compound 
engine, it is apparent that by introducing the other cylinders 
in the multiple-expansion type certain disadvantages are intro- 
duced. These are: 



142 MECHANICAL ENGINEERING OF POWER PLANTS, 

1. The cost of the cyHnders other than the low. In tan- 
dem engines this may mean the cost of piston and cylinder 
with additional rod, but in cross-compound and fore-and-aft 
engines it means an additional cost of practically another 
engine with crank, connecting-rod, cross-head, and the like. 

2. The weight and bulk of the additional cylinder adding 
to foundations and taking up valuable space. 

3. The friction-loss due to the work absorbed by this extra 
cylinder in operating its mechanism, valve, and the like. 

4. The loss by radiation of heat from the surface of the 
extra cylinder and valve-chest, which are surfaces exposed to 
the air. 

5. The loss of work due to the diflficulties discussed in 
pars. 65 and 6'j , represented by lost area in the work-diagram 
from friction, free expansion, condensation, and the like. 
The single-engine diagram, getting the same grade of expan- 
sion in the same cylinder, would not experience this. 

6. The difficulty connected with regulating the power of 
the engine when the work varies widely, and the first cylinder 
has measured off a volume of steam adapted to a resistance 
different from that upon the engine when that volume of 
steam reaches the later cylinders. This is the difficulty of 
governing the multiple-expansion engine, except by regulat- 
ing devices operating upon each cylinder independently. 

7. There has been considerable trouble in compound 
engines from the accumulation of water in the low-pressure 
cylinders, particularly when compounding above the atmos- 
phere and using wet steam. The wide range of expansion, 
the lowered terminal pressure, and the large diameter of the 
low-pressure cylinder have made this difficulty a very trouble- 
some one in locomotive practice. 

It is obvious that the weight to be attached to the 
above objections is not considered by most designers to be 
great enough to overbalance the advantages which follow from 
the principle of compounding. 

72. Proportion of Compound-engine Cylinders. — It 
would be foreign to the present purpose to enter deeply into 



SIMPLE AND COMPOUND ENGINES. I43 

the question of the design of compound engines. It may be 
said that when the conditions indicate that it would be desir- 
able to cut off later than one third of the stroke so as to have 
less than three expansions, there would be no gain from carry- 
ing boiler-pressure very much higher than 80 pounds above 
the atmosphere, and that the conditions point to the use of a 
single-cylinder engine. The following table presents accepted 
practice with respect to a selection of the grade of expansion 
with fixed boiler-pressures. 

When the values for T^ are those which belong to a 
pressure below 80 lbs., use single engine; 

for pressures between 80 and 100 lbs. '^ compound engine; 

130 and 160 '' '' triple 
** *' above 170 lbs. ** quadruple *' 

Usual cylinder-ratios of practice for usual pressures with 
triple engines, are: 

Pressures. Small. Intermediate. Large. 

130 I 2.25 5 

140 I 2.40 5.85 

150 I 2.55 6.90 

160 I 2.70 7.25 

170 Quadruple engine preferred. 

For quadruple-expansion engines the usual ratios of cylin- 
der-areas and volumes approximate i : 2 : 3.78 : 7.70, which 
may be called 1:2:4:8. 

If the principle be adopted that the ratios of areas are to 
be as the fourth root of the number of expansions, the ratio 
of the first to the fourth will be as the cube of the fourth root. 
The ratio will increase as the initial pressure becomes greater; 
€.g., I : 2.2 : 4.8 : 10.6. 

Mr. G. I. Rockwood has designed a compound engine 
with a cylinder-ratio of 7 : i with the view of making heat- 
range equal in the two cylinders, whereby the ratio of surfaces 
is taken account of, as well as the differences in temperature. 



CHAPTER VI. 

SUNDRY CLASSIFICATIONS. CONTROL OF ENERGY. 

73. Review and Introductory. — The preceding chapters 
and paragraphs have treated the steam-engine from the points 
of view first of typical mechanism, and second of the use of 
steam in engines. These are not the only convenient classifi- 
cations, but are believed to be the most valuable as foundations 
for inductive study. A very usual and convenient classifica- 
tion may be based upon the service or use to which the engine 
is to be put. This would give rise to the following three 
classes : 

(a) Stationary engines; 

(d) Locomobile engines; 

{c) Portable engines. 

The stationary-engine class would be subdivided into fac- 
tory or mill engines, including power-house engines; pump-^ 
ing-engines, including blowing-engines and air-compressors; 
hoisting-engines; and miscellaneous engines. The locomobile 
engines would include locomotives, traction engines, including 
road-rollers and self-propelling steam fire-engines, and engines 
for marine propulsion. The portable-engine class would 
include a wide variety of engines, designed principally for 
agricultural service, which are intended to be moved about 
upon their own wheels, so as to be ready for use at the place 
where they may be. Their design is such that the engine and 
the boiler are self-contained, and no foundation or permanent 
structure of any kind is required. Fig. no presents the 
usual type of engine of this class. Sometimes engines of 
small size are termed semi-portable when their construction is 

144 



SUNDIiY CLASSIFICATION'S. CONTROL OF ENERGY. 1 45 

such that their weight is not excessive, and they are self-con- 
tained to the extent that a provisional or temporary founda- 
tion of timbers or skids is all that they require as substructures. 
In view of the relatively accidental character which the 
resistance bears to the work of the steam, the above sub- 
divisions are merely mentioned without further comment. 
When the engine is to be specifically designed with respect 
to the resistance, as in pumping, rolling-mill engines, locomo- 




FlG. I TO. 

tive and marine practice, then the study of the resistance 
properly becomes the subject of prime importance and must 
be specifically investigated. For the purpose in hand, which 
is restricted to the investigation of the steam part of the 
engine, these considerations open too wide a field to be entered 
upon, and the reader must be referred to specific treatises. 

74. Control of Energy of the Steam in an Engine. 
Throttling-engines. — A division of steam-engines into 



14^ MECHANICAL ENGINEERING OF POWER PLANTS, 

classes, which possesses both interest and importance is based 
upon the method to be followed in controlling an engine with 
respect to the energy which it shall deliver in a unit of time, 
and when the resistance may vary within wide limits. Refer- 
ring again to the formula for the horse-power (par. 6), 

H.P. = ^^ 

33,000 

or 

Yi.Y,^PKN. 

It will be remembered that K replaces the constant factors 
AL divided by 33,000, which cannot be altered when the 
engine has been once designed and the cylinder made. In 
engines designed for many types of service the number of 
revolutions in the minute should be kept the same, or iV a 
constant. Hence, when the resistance varies and the energy 
of the engine is also to vary to maintain equilibrium, the 
mean pressure P prevailing in the cylinder must be the factor 
which is made to vary. It can be made to vary in two ways, 
and the method pursued to produce this change in P gives 
rise to two great classes of engines. 

The energy stored in the vapor of water by heat in the 
form of elastic tension comes over into the engine-cylinder 
through a pipe or passage. A valve in this pipe or passage 
when closed entirely will serve to shut off the engine from 
its reservoir of energy (the boiler). When partly closed by 
such a valve the passage between the engine and boiler 
is choked or throttled, and hence this valve has been called 
the throttle-valve. An engine whose design is such that 
the value for P in its horse-power formula is diminished by 
closing such a throttling-valve, or increased by opening it 
wider, is called a throttling-engine. The effect of this process 
of throttling upon the diagram of effort (par. 44) is to diminish 
the length of the vertical ordinates, and diminish in this way 
the area of that diagram, and hence the foot-pounds of work 
per stroke. Fig. 1 1 1 shows several diagrams superposed in 
which the variation of area is secured by lowering the average 



SUNDRY CLASSIFICATIONS. CONTROL OF ENERGY. 1 4/ 

lieight of the card. The opening and closing of a throttling- 
valve in the steam-pipe of a throtthng-engine is usually 
effected by a mechanism which, from its function to govern 




the pressure in the cylinder, is called a steam-engine governor. 
The features of this mechanism will be discussed in the sequel. 

75. Cut-off Regulation of a Steam-engine. Cut-ofl 
Engines. — It will be apparent from inspection of the diagram, 
Fig. (ij., P3-^' 44> that it will be possible to diminish the area 
of such work-diagram by diminishing the proportion of the 
stroke during which admission of steam occurs. By shorten- 
ing the length of the upper line of the diagram (Fig. 112) it 
will be obvious that the same effect in diminishing the energy 
of the stroke will be produced as if the height of the diagram 
had been shortened, as explained in the preceding paragraph. 
It will be observed that the pressure of the steam which enters 
the cylinder has not been reduced or throttled by closing an 
opening, but that the steam is permitted to enter the cylinder 
at full pressure, but for a longer or shorter time, according as 
the work to be done has increased or diminished. In other 
words, engines of this class vary the point of cut-off to regulate 
their energy, and are therefore called variable cut-off engines. 

All engines require a mechanism adapted to admit the 
steam at one end of the cylinder, and exhaust it at the 



148 MECHANICAL ENGINEERING OF POWER PLANTS. 

other at proper intervals. This mechanism is called the 
valve-gearing, and has for its function the distribution of the 
energy and pressure to the working face of the piston. All 
engines, whether of throttling or cut-off regulation, will have 
an independent throttle-valve under the control of the engine 
runner or driver. 

In the variable cut-off engines the adjustment of the length 
of the period of admission can be done either by hand, or it can 
be arranged that this variation shall be effected automatically 
by a mechanism for this purpose. When the variation of ad- 




mission or of the point of cut-off is made by hand, or through 
the intervention of a human intelligence, the engine is called a 
variable or adjustable cut-off engine. Where the variation in 
the period of admission is made by an automatic mechanism 
(usually a governor), the engine is called an automatic cut-off 
engine. The opening and closing of the distributing-valves is 
always effected by the engine itself in modern engines, and in 
this sense all engines are automatic. But when the mechan- 
ism causes the time at which the cut-off occurs to be varied 
automatically the term automatic cut-off becomes applicabJe. 
76. Advantages and Disadvantages of th« Throttling- 
engine. — An engine designed to have the pressure varied 
upon the piston by throttling the steam-pipe conveying the 
energy offers the following advantages: 



SUNDRY CLASSIFICATIONS. CONTROL OF ENERGY, I49 

1. The engine is cheap to build and to buy. The valve- 
gear for distribution will be simple and therefore inexpensive, 
and the governor controlling pressure only will be extremely 
simple, and its valve need not be complicated. 

2. The effort of the steam to drive the piston will be 
exerted through a considerable portion of the stroke. Hence 
there will be less inequality in the steam effort at the begin- 
ning and end of the stroke. 

3. The effect of driving the steam through the throttling- 
valve or orifice is to bring about the equivalent of a super- 
heating of the steam. The pressure on the boiler side of the 
valve is greater than that on the cylinder side. Hence if the 
steam were saturated at the higher pressure, it will have a 
temperature on the low-pressure side higher than belongs to 
that pressure, and is therefore in a superheated condition. 
This has a tendency to dry out moisture in the steam and to 
■diminish condensation in the cylinder. The heat correspond- 
ing to friction in the throttle-valve area must also appear in 
the form of heat, some of which serves to heat and dry the 
steam. 

4. The throttling-engine for these two latter reasons is 
likely to suffer less from cylinder-condensation. The dimin- 
ished range of temperature between the two ends and the 
relatively higher terminal pressure are the reasons for this. 

The disadvantages of the throttling-engine are the advan- 
tages for the cut-off type. They are: 

1. It is not as sensitive as the cut-off engine to instan- 
taneous variation in the resistance. The control by throttling 
can only take effect in the cylinder at an interval after the 
governor has acted to throttle the steam or to open the valve 
wider. The engine meanwhile has had a chance to make at 
least one stroke under the conditions which prevailed before 
the change of condition was announced to the governor. 

2. The throttling-engine does not regulate as closely to 
uniform speed as the cut-off engine. The reason for this is 
partly that explained in the preceding sentences, and partly 
because the method of controlling by the motor fluid in bulk 



ISO MECHANICAL ENGINEERING OF POWER PLANTS. 

cannot be expected to be as exact as when the control is 
exerted immediately upon each reciprocation of the piston. 

3. The exhaust will usually be at a higher pressure in a 
throttling-engine, causing the rejection of more heat from the 
cylinder than when, by early cut-off and high expansion, the 
heat is more completely withdrawn from the steam in the 
form of work. 

77. Advantages and Disadvantages of the Cut-off 
Engine. — When the regulation of effort is secured by causing 
the length of the admission period to vary either automatically 
or by hand and without diminishing the initial pressure, the 
following advantages are secured: 

1. The effort is controlled per stroke of the piston. Just 
enough steam is admitted into the cylinder to do the work of 
that stroke. 

2. For this reason the engine is sensitive immediately to 
variations of the resistance. 

3. It is more certain to be kept by the governing appliance 
at the uniform or fixed speed, since a variation caused in the 
governing appliance operates immediately to control the 
admission for the next stroke. 

4. The full energy present in the elastic tension of the 
steam as it comes from the boiler is exerted upon the piston 
without undergoing the loss from throttling. This may or 
may not be considered an advantage (see par. 'j6 above). 

5. The cut-off engine derives full advantage from the prin- 
ciple of expansion and the gains from expansive working (see 
par. 44). Lower terminal pressure causes less heat to be 
rejected into the exhaust, and reaps the full advantage of hav- 
ing as great a difference between the initial and final pressure 
and temperatures of the steam in the cylinder as is consistent 
with doing the foot-pounds of work required for that stroke. 

The disadvantages of the cut-off engine are the contradic- 
tories of the advantages of the throttling-engine: 

I. There is a wide difference in the pressure and effort at 
the two ends of the stroke when the engine is working with an 
early cut-off. This compels a massive fly-wheel to take care 



SUNDRY CLASSIFICATIONS. CONTROL OF ENERGY. 151 

of these wide variations, and to give out in the latter part of 
the stroke the excess of work stored in it at the beginning. 

2. The design and compHcation of valve-gear to provide 
for properly varying the admission. 

3. This complication usually makes the engine costly to 
build and to buy. If closeness of regulation without the inter- 
vention of human agency is not worth paying for, the superior 
economy of the automatic cut-off engine does not always pay 
the interest on the difference of first cost. 

4. The lower value for the terminal temperatures and 
pressures increases the amount of cylinder-condensation by 
reason of the better opportunity for the evaporation of mois- 
ture present in the cylinder either mechanically entrained or 
as the result of radiation or the doing of work. The evapo- 
ration of such moisture under reduced pressure makes the 
demand for the necessary heat for vaporization from either the 
working steam or the metal of the cylinder. It is this condi- 
tion which accounts for the result experimentally found, that 




Fig. 113. 

in non-condensing engines, such as the locomotive, it does 
not pay to carry the expansion further than is given with the 
cut-off at one third of the stroke. 

5. It may happen when the engine is very lightly loaded 



^52 MECHANICAL ENGINEERING OF POWER PLANTS. 

that the cut-off will take place so early that the final volume 
of the cylinder will be greater than that which the volume of 
steam admitted would fill at the pressure of the exhaust- 
stroke. The line representing pressures will therefore cross 
the line representing the return-stroke before the stroke is 
completed, forming a loop at one end (Fig. 113). The area 
inclosed in that loop is a negative v/ork in a single-cylinder 
engine and represents a pumping-action of the piston, be- 
cause when the exhaust is open the material in the exhaust- 
pipe would have a tendency to fiow back into the cylinder 
instead of away from it. In compound or continuous-expan- 
sion engines the area of this loop represents expansion of the 
steam in the receiver or clearances doing no work, and is 
therefore a distinct loss. 

• 78. Summary and Conclusions. — For many classes of 
work in power-house service the variation of resistance is so 
wide and so rapid that it would be inconvenient or impracti- 
cable to depend on human quickness of perception to provide 
for it. On the other hand, where the effort is constant, as in 
pumping, or is progressively varying, as in hoisting from deep 
mines, and in railway and marine practice, the other method 
of regulation is close enough to be satisfactory, and particularly 
where the engine-runner must be in attendance in any case. 
The automatic cut-off engine is usually the more economical 
of the two, but it is not a settled question whether all of this 
economy is due to the method of regulating. The automatic 
cut-off engine is usually better built in every way, and such 
excellence of construction would explain some of its economy. 
It would be apparent, therefore, that the appliances for 
affecting regulation of effort are the next questions to be con- 
sidered in developing the steam-engine, and that therefore 
the valve-gearing and the governor present themselves for 
study. As the governor must be interdependent upon the 
valve-gearing, while the latter may be independent of the 
governor, the valve-gearing for steam-engines will form the 
subject of the next chapter. 



CHAPTER VII. 
VALVES AND VALVE-GEARING. 

79. Introductory. — The earliest steam-engines were oper- 
ated entirely by the throttle-valve. A single valve in the 
proper pipe was opened and closed (by hand at first) so that 
-energy was admitted and exhausted at will. The idea of 
having the valve for the cylinder self-acting and driven by the 
moving mechanism is attributed to a lad named Humphrey 
Potter. He attached the handle of the cock-valve or faucet 
then used for this purpose to the rising and falling rods of an 
early pumping-engine as far back as 1713. The rude scoggan 
•or catch with cord connection originated by Potter was 
improved by Henry Beighton (17 18), and the tappets and 
catches characteristic of the Cornish engine were modifications 
of these early ideas. 

The functions of the valve or valves which distribute 
steam in a steam-cylinder are primary and secondary. The 
primary function is to admit the steam from the boiler to one 
side of the piston, while the exhaust-steam filling the other 
end of the cylinder is permitted to escape with the least possi- 
ble resistance. The secondary functions are to close the 
admission of steam at the point necessary to give the expan- 
sion desired, and to close the exhaust-orifice at such a point 
in the return-stroke that a certain volume of steam shall be 
caught and compressed behind the piston, so that when the 
return-stroke is completed there may be caught between the 
piston and the head of the cylinder a volume of steam to 
serve as an elastic cushion. The ideal final tension of this 
entrapped steam-cushion should be that of the steam in the 
boiler or the valve-chest. 

153 



154 MECHANICAL ENGINEERING OF POWER PLANTS. 

The opening of the inlets and outlets of the cylinder 
should be so timed with respect to the stroke of the piston 
that pressure may not be brought too soon against the piston- 
head, nor the exhaust opened until the expanding steam has 
done its entire work for that stroke. 

The valves for admitting and distributing steam in an 
engine-cylinder may open the ports which they control either 
by lifting from their seats or by sliding upon their seats. 
Hinged or flap valves are not used for steam-engines. When 
the engine is a double-acting one there must be provision to 
connect each end of the cylinder with the boiler and each end 
with the exhaust-pipe. When the engine is single-acting it 
is only necessary to connect one end to boiler and exhaust-pipe 
alternately. Apparently the simplest arrangement would 
be to have four valves — one at each end for steam and one at 
each end for exhaust. This principle is represented in the 
usual river-boat steam-engine (Fig. 30), and in the ordinary 
Corliss engine and its derivatives. 

A second great type makes use of separate valves for 
admitting steam at the two ends, but the exhaust-outlets for 
both ends are controlled by one single valve. Such engines 
are called three-valve engines. 

The third arrangement is to have one valve for admitting 
steam to both ends and another controlling the exhaust from 
both ends. An engine of this type is the Porter-Allen- 
Such engines are called two-valve engines. 

A fourth class have one single valve so designed as to take 
care of inlet and outlet functions for both ends. Such are 
the great majority of steam-engines for stationary use, all 
locomotives and marine engines. The great importance of 
the single-valve engine and its wide distribution form the 
reason for considering it in advance of other form.s. 

80. Three-way and Four-way Valves. — It will be appar- 
ent when one end of a cylinder is to be put into alternate 
communication with boiler and exhaust-pipe that the ordinary 
three-way valve can be made to fill these requirements by 
causing it to vibrate through an angle of 90°. Fig. 120 



VALVES AND VALVE-GEARING. 



155 



shows the position of the plug of such a cock when the steam- 
pipe from the boiler is to be connected to the cylinder, and 

FROM BOILER 



FROM BOILER 




TO CYLINDER 

Fig. 120. 



FROM CYLINDER 

Fig. 121. 



Fig. 12 1 shows the position 90° distant when the cylinder has 
been connected to the exhaust-pipe. It will be seen that the 



FROM BOILER 



FROM BOILER 




TO EXHAUST 



Fig. 122. 



Fig. 123. 

motion which connects the cylinder with one opening closes 
its connection with another. 

It is not difficult to modify the three-way cock that it may 



156 MECHANICAL ENGINEERING OF POWER PLANTS. 

serve to distribute steam in and out of both ends of a double- 
acting engine. It is only necessary to make the valve a 
four-way valve as shown in Fig. 122, and the alternate vibra- 
tion of such a cock from the position shown in Fig. 122 to 
that in Fig. 123 is all which is required to enable such a valve 
to discharge the primary functions of a valve-gear. The 
rocking or vibrating motion of the plug needs only to be so 
timed with respect to the crank-motion that the admission 
and exhaust functions may begin and end for each end of the 
cylinder when the piston and crank are on their dead-centres. 
y, The vibrating or plug valve as the distributing- valve is a 
very early form, and is still used in its old form in some small 
engines for the sake of cheapness, and in a modified form in 
some large and elaborate designs. The objections to the old 
plug cock-valve are: 

1. The valve and its casing cannot usually be cylindrical, 
because unequal expansion by heat is apt to cause the casing 
to seize the plug with a firmness which will cause valve-rods 
and pins to buckle .and shear before the valve will turn. This 
occurs because the casing is exposed to radiation to the outer 
air and protects the plug from its action. The plug will 
therefore be hotter than the casing, and if fitted snugly when 
cold they will seize together when hot. 

2. If fitted loosely enough not to seize, cylindrical plug- 
valves will leak. To prevent this they are usually made 
slightly taper, so that just the necessary friction and tightness 
may be secured by adjusting the plug lengthwise in its conical 
seat or casing. These taper fits are not so easy to make 
perfect except with special machinery. Even then in large 
sizes the large end expands more than the small, and for a 
given angular motion the large end slides over a greater space 
than the small. This tends to produce unequal wear and 
leakage. The taper plug can be refitted to its seat when 
worn, which cannot be done with a cylindrical fit. The taper 
is usually one in sixty-four or thirty-two. 

The vibrating-valve can be made, however, into a very sat- 
isfactory arrangement by either making the plug proper a shell 



VALVES AND VALVE-GEARING. 



157 



which is independent of the axis of the cylinder in which it 
turns — this is the CorHss valve — or else by cutting away all of 
the plug except just the surface required to close the opening 
through the casing which the valve must control. This is a 
feature of the Wheelock valve and of many derivatives and 
modifications of the Corliss (see Fig. 181). They present the 
advantages which belong to an arrangement which opens a 
wide area by a comparatively small motion of the valve. 

Another method of avoiding the difificulties of the cylin- 
drical or conical valve is derived by enlarging the radius of the 
casing of the valve until it becomes infinity, when the valve- 
seat becomes a plane and the vibration of the plug becomes 
a straight translation or sliding of a block upon a flat surface. 
The great advantage of the flat slide-valve and seat is the ease 
and certainty with which plane surfaces can be made in practice, 
and that when the two surfaces are true and of homogeneous 
material the sliding of the valve upon its seat tends to wear 
the contact always closer and diminish leakage. It is this 
practical consideration which has had much to do with the 
abundant distribution of the fiat sliding-valve. The construc- 
tion of the lifting-valve will be referred to hereafter. 

81. Plain Slide-valve working Full Stroke. — It will be 
apparent from Fig, 124, which represents a four-way cock 




Fig. 124. 



Fig. 125. 



developed upon a plane in the ordinary form in which it is 
used in practice, that there is present the inlet from the boiler 
coming in to the top of the box which will be called the valve- 
chest in which the valve moves. Passing outward from below 
in the middle of the developed surface on which the valve 



158 MECHANICAL ENGINEERING OF POWER PLANTS. 

seats is the exhaust-pipe orifice; it has become the exhaust- 
port on the valve-seat. The two other inlets into the valve- 
seat which were present as radial openings in Figs. 122 and 
123 appear in Figs. 124 and 125 as ports or openings one at 
each side of the central line of symmetry through the steam- 
pipe and exhaust-port. 

As the valve stands in Fig. 125, its length from out to out 
horizontally is just the length from out to out of the steam- 
ports. Both ports are closed, but the motion of the valve in 
either direction will cause steam from the boiler to pass into 
one or the other of the ports to reach the end of the cylinder 
and drive the piston. It would appear then that the position 
of the valve shown in Fig. 125 is that which belongs to the 
two dead-centres of the piston. 

It will be further seen that the hollow in the under side of 
the valve has a net length the same as the length between the 
inner edges of the steam-ports. Hence when the valve moves 
in either direction so as to admit steam by its outer edge to 
either steam-port, by that same motion the port at the other 
end is opened by the inner edge to allow steam to escape from 
the other end of the cylinder into the hollow of the valve 
which is always in connection with the exhaust-port and pipe. 
The distance between the edges of the steam-ports out to out 
is immaterial within limits, since the only effect of separating 
these outer edges is to lengthen the valve. To do so, how- 
ever, is to increase the area upon which pressure of steam acts 
to press the valve to its seat, and hence to increase the force 
necessary to slide the valve. The width of the ports is fixed 
by the area which they must have in order to pass the steam 
Avhich the engine requires per stroke without imposing an 
excessive linear velocity for that steam. The length of the 
port in the direction perpendicular to the plane of the paper 
is conditioned by the diameter cf the cylinder, which of course 
it cannot exceed. It can at best be equal to that diameter, 
but it is more usual to make it somewhat less. With the 
length thus fixed the area of the port should be such that the 
linear velocity of the steam through the port should not 



VALVES AND VALVE-GEAKING. I $9 

exceed 100-150 feet per second, or 6000-8000 feet per 
minute. Simple calculations for this area in terms of the 
horse-power of the engine appear in the appendices. 

It is of advantage not to make the port too wide in the 
direction of the motion of the valve to the right or left, since 
it will be apparent that the motion of the valve from this 
central position to the right or left should be equal to the 
width of the port in order to open it wide. In other words, 
the throw of the valve and the port width should be the same 
under the conditions now being considered. If the valve- 
throw from its central position is greater than the port width, 
an unnecessary force is expended to slide the valve. If the 
port width is not uncovered by the throw of the valve, an 
unnecessary surface is exposed below the valve to the steam 
on its way from the valve to the piston, causing losses by 
radiation, by contact, by condensation, and by unnecessary 
clearance-volume, which the steam fills to no purpose. The 
throw of the valve is the distance which it moves from its cen- 
tral position in each direction. The travel is the distance 
which it moves from its extreme position at either side to the 
other extreme position, and is therefore twice the throw. 
If the valve is operated by a crank or a modification of it, the 
radius of the crank will be equal to the throw, and also equal 
to the port-opening. It is susceptible to demonstration that 
the volume of the cylinder and the area of the port-opening 
increase according to the same law when the motion of each 
is controlled by a crank; but the exceeding convenience of 
the crank induced its adoption before this theoretical pecu- 
liarity had been elaborated. 

82. The Eccentric is a Crank. — The throw of most en- 
gine-valves will be comparatively small as compared with the 
stroke of the piston; and, in engines of considerable size, 
when the shaft is of a large diameter it becomes incon- 
venient and impossible to cut away the large shaft so as to 
get the small crank in the middle of it. It is furthermore 
inconvenient to drive the valve in most engines from a crank 
at the end of the shaft. It does not affect the peculiarity of 



l6o MECHANICAL ENGINEERING OF POWER PLANTS. 

a crank to enlarge its pin. So that if the typical crank AB 
shown in heavy lines in Fig. 126 have its crank-pin succes- 
sively enlarged until the diameter of the latter becomes so 
great that the circle representing it surrounds the shaft which 
is the centre of motion of the crank, there will be no differ- 
ence produced in the motion of such a pin as it revolves around 
the original centre of motion. The enlargement of the pin 
has produced an eccentric, in which the distance between the 
centre of motion and the centre of figure is the radius of the 
original crank. The valve driven by an eccentric is therefore 




Fig. 126. 

driven by a crank, and the use of an eccentric not only makes 
it unnecessary to cut away and weaken the engine-shaft, but 
has the further advantage that the direction of the centre-line 
of the crank can very easily be changed with respect to the 
engine-crank, should it be desirable to alter and adjust 
the angular relation between these two. When valves are 
not driven by a crank or eccentric, it will be found that the 
motion will be given either by cams or by such a combination 
of rods or links as to constitute a link-motion. These methods 
of driving valves will be discussed in proper course. Fig. 4 
shows the valve driven by a crank from the end of the shaft, 
but in the majority of engines where the valve is driven, 
directly it will be found that the eccentric is used. 



VALVES AND VALVE-GEARING. l6x 

83. Setting of a Plane Slide-valve working Non-expan- 
sively. — From an inspection of Fig. 124 it will be observed 
that the valve has the shape somewhat like\ letter D, resting^ 
with its straight side upon the seat. For this reason this 
valve has been called the D slide-valve (the German name is 
Muschelschieber, or shell-slider). It will be observed that if 
the piston is at its dead-centre at the right of the page in Fig. 
125, the valve should move towards the left to admit steam 
to drive it. If the piston is at the left of the page, the valve 
should move towards the right. It has been further shown 
that when the engine-crank is at one of its dead-centres, and 
in a horizontal line in a horizontal engine, the valve is in its 
central position with its crank therefore standing vertically 
up and down. The fair conclusion then is that in an 
engine working non-expansively the valve-crank is 90® 
distant from the engine-crank. Is it to be 90° ahead or 
behind ? 

When the engine throws over (par. i i),and the piston is 
on its dead-centre at the right of the page, it is obvious that 
the valve has been at its right-hand end and has returned 
to its central position from the right to reach the position 
shown in Fig. 125. This follows because it has been admit- 
ting steam for the stroke of the piston from left to right, and 
has closed the port at the left at the end of the stroke hyr 
coming from the right. It is therefore to admit steam to the 
right-hand port by moving towards the left, which it can only 
do when the crank driving the valve is standing vertically 
upwards. It is assumed that the engine-shaft is at the left as 
the observer faces Fig. 125, and that the rotation is contrary 
to the hands of a clock. It is further assumed that the length 
of the rod connecting the valve-crank or eccentric to the valve 
is of exactly the right length, and that the valve is connected 
to the eccentric without the interposition of a vibrating arm or 
rock-shaft, which would reverse the motion imparted by the 
valve-crank. Under these assumptions the valve or crank is 
to stand with its centre-line making an angle of 90° with the 
engine-crank ahead of the engine-crank in the direction in 



1 62 MECHANICAL ENGINEERING OF POWER PLANTS. 

which the engine is to turn. Hence the directions for setting 
the valve for a non-expansive engine of this sort are: 

1. See that the valve-rods are of the right length so that 
the valve opens the ports equally at both ends of its throw. 
This is called making the valve run square. 

2. Set the main crank of the engine on either dead-centre. 
This can be done either by eye, or more exactly by the fol- 
lowing process. Turn the engine over until the crank is 
nearly at its dead-centre and scratch a mark on cross-head and 
guide which shall indicate such position. Take a beam-com- 
pass or trammel, such as shown in Fig. 127, and put one 
point in a centre-punch mark made on the rim of the fly- 
wheel while the other end rests on a similar prick-punch mark 
on the frame or bed-plate of the engine. Then turn the 
engine-crank past its centre until the mark scratched on cross- 
head and guides comes to coincidence again, and the trammel 
in the fixed point on the bed-plate locates by its other end a 
second point in the fly-wheel rim. It is apparent that the 
first and second of these points in the rim indicate two 



r^^^=\ 



Fig. 127. 

angular positions equally distant from the dead-centre on 
opposite sides of it. The point half-way between them on 
the rim should be the point in which the same trammel stand- 
ing with one end in the fixed point on the bed-plate should 
reach when the engine is on its true dead-centre. 

3. Slip the eccentric around the shaft in the direction in 
which the engine is to turn until it is 90° ahead of the engine- 
crank, if this can be observed. If not, it is reached when the 
valve is in its central position, line and line with the edges 
of the steam-port. Then the eccentric is made fast. 

4. Turn the engine through 180° to bring the main crank 
at its other dead-centre to test the accuracy of the adjustment. 

If the engine has a rock-shaft which reverses the motion 
from the eccentric, the eccentric should be set 90° behind 



VALVES AND VALVE-GEARING, 1 63 

the engine, or at a position 180° distant from that which it 
occupies when the motion is direct. 

If the engine throws under instead of over, the eccentric 
is still 90° ahead of the crank, in the direction in which the 
engine is to turn, but is 180° distant from the position which 
it occupies when the engine throws over. 

The expansion of the valve-rod by heat must not be over- 
looked in its effect upon the length of such rods. It will 
lengthen the rods of a valve directly connected, and either 
lengthen, shorten, or be without effect upon the rods which 
are connected to a rock-shaft. If the rod from the eccentric 
to the rock-shaft and from the rock-shaft to the valve were 
of the same length and of the same temperature, the effect 
of expansion would be compensated. 

84. The B Valve. — In some forms of engines, particularly 
pumps, it is desirable that the motion of the valve to admit 
steam should be in the same direction as that which the piston 
had before it completed its stroke. In the D valve these 
motions are opposite. The valve to meet this condition must 
differ slightly from the D valve in its shape, and from the form 
which it takes it is called the B valve (Fig. 128). It admits 




Fig. 128. 

steam into the one hollow of the B by sliding past the end of 
the seat or over the edge of an outer port. The other hollow 
is by this motion put into communication with the other 
steam-port and the exhaust, so that its functions are the same 
as those of two D valves, with the exception that the outer 
edge of the valve does not act. The details for setting the 
directly connected B valve are the same as for setting the D 
valve with rock-shaft. 



164 MECHANICAL ENGINEERING OF POWER PLANTS. 



85. Lap in the Slide-valve. — It will be observed from 
Fig. 125, and the proportions of valve and seat as there 
presented, that there is no interval during which admission of 
steam does not take place at one end of the stroke or the 
other, except the instant of passing the two dead-centres. 
The diagram of effort in a cylinder thus controlled would be 
that shown in Fig. 66, which presents the work of a cylinder 
without expansion. Admission and exhaust take place 
throughout the full stroke. It has been seen that this is not 
usual or desirable, but that there should be a period tow^ards 
the end of a stroke during which steam enclosed in the cylin- 
der should have an opportunity to expand and lower its 
pressure. This must be secured by cutting off admission, or 
leaving a period in the motion of the valve during which both 
steam-ports shall be closed from connection with the boiler. 

The valve of Fig. 125 cannot be made to do this by 
reason of its length being only that from out to out of the 
ports. The valve must be lengthened in order that it may 
close one port and be still sliding upon its seat while the 
piston is moving towards the end of its stroke, and so that it 
shall just reach the position of opening the new port at the 
other end as the piston comes to rest at the dead-centre. 
This addition of length must be symmetrical on both sides of 
the centre-line, and the increase at each end over the funda- 
mental length of the non-expansive valve is called its lap, ab 
in Fig. 129. 




Fig. 129. 

Lap may be defined as the amount which the valve stand- 
ing in its central position projects over or laps beyond the 
outer or steam edge of the port. 



VALVES AND VALVE-GEARING. 1 65 

86. Effects of the Lap. — The effects of the lap are: 
I. To compel the steam in the cylinder to work expan- 
sively, or to produce the cut-off of admission before the end 
of the stroke. It will be apparent from Fig. 130, which shows 
a valve on its seat moving from right to left and distant from 
its central position a distance equal to the lap on the left- 
hand end, that it has just cut off admission from the left- 
hand end of the cylinder, and must move to the left through 
a distance equal to twice the lap before it can open the right- 
hand port. It must open this latter port at the instant that 
the piston is ready to begin its stroke from right to left. 




Fig. 130. 

Consequently the piston will have moved without admission 
during a period of angular motion at the end of its stroke 
corresponding to that required to move the valve through 
twice the lap. This is an angular motion corresponding to 
twice the angle whose sine is the lap. This being so, the 
instructions for setting the slide-valve without lap or without 
expansive working (p^^'- ^3) require to be modified. The 
valve-crank or eccentric is ahead of the main engine-crank 
not only the 90° there deduced, but is to be ahead 90° -f- an 
angle whose sine is the lap. 

2. Hence the second effect of the lap is to set the valve- 
crank forward and prevent the valve being in its central 
position when the engine is at its dead-centre. 

3. The consequence of this second peculiarity is that the 
-opening of the exhaust hollow in the valve to the two ends 
of the cylinder becomes displaced, and does not take place as 
heretofore when the engine passes its centres. The exhaust 
on the expanding or completed stroke is preopened, because 
the valve passes its central position before the piston reaches 
the end of its stroke. It must do this because it has to slide 



l66 MECHANICAL ENGINEERING OF POWER PLANTS. 

through a space equal to the lap in order to open the valve 
at dead-centre for the ensuing stroke. This has also preclosed 
the exhaust-port at the right-hand end by the same action 
and for the same reason. The preclosure of the exhaust is of 
no great disadvantage within limits, inasmuch as by this action 
the entrapped exhaust undergoes compression after its outlet 
is closed and there is produced the cushion which was referred 
to as desirable in par. 79. The preopening on the expanding 
side, however, is absolute loss, since tension of the driving 
steam which should have followed the piston clear to the end 
is released into the exhaust, and is wasted. 

87. Inside Lap. — When the term lap is used without 
qualification it means lap added to the outside or steam edges 
of the valve. In order to prevent prerelease of the expanding 
steam, from too early opening of the hollow of the valve to 
the steam-port, the valve-face can be widened towards the 
inside by adding metal which shall narrow the opening into 
the hollow. The normal valve has its hollow of the same 
length as the distance between the inner edges of the steam- 
ports. When the valve stands in its central position, the dis- 
tance by which the length of the hollow is less than the dis- 
tance between the inner edges of the ports amounts to twice 
the inside lap. Or, in other words, the inside lap is the dis~ 
tance which the valve must move from its central position 
in either direction in order to open the corresponding end of 
the cylinder to the exhaust-port (see cd. Fig. 129). 

88, Effect of Inside Lap. — The effects of inside lap are : 

1. To prevent prerelease of expanding steam before the 
stroke is completed. 

2. To close the exhaust-outlet from the cylinder before 
the exhaust-stroke is completed. This produces a compres- 
sion. The effect of this compression on the practical working 
of the engine is fourfold. 

(1) It serves to produce a spring or cushion of elastic 
steam which serves to absorb living force in the reciprocating 
parts and bring the latter to rest by a gradual force exerted 
to take up lost motion in the joints in the direction in which 



VALVES AND VALVE-GEARING, 167 

the next working stroke is to strain them. Without this 
cushion the Hving force of the reciprocating parts must be 
absorbed by the crank-pin, which will produce tension on the 
joints just previous to the compression-stroke, and compres- 
sion of the joints just previous to the tension-stroke. The 
steam-cushion makes the engine run more quietly. 

(2) This compressed steam after exhaust-closure fills the 
clearance and port passage with steam otherwise wasted, so 
that the entering steam when the valve opens does not have 
to fill such waste room. Generally the compression should 
be so calculated that the final pressure of the steam com- 
pressed into the clearance-volume just equals the pressure of 
the steam coming from the boiler. 

(3) The compression caused by inside lap exerts an upward 
pressure upon the valve which tends to counteract the down- 
ward pressure from the boiler, and thus makes the valve move 
more easily upon its seat for that part of the stroke during 
which the compression occurs. 

(4) The effect of the compression of the exhaust-steam is 
to raise its temperature and with it the temperature of the 
cylinder-walls. This heat is due to the absorption by the 
steam of the work done in compressing it, and consequently 
the entering steam on the new stroke undergoes less conden- 
sation in heating the metal. 

Excessive compression due to excessive inside lap or too 
early closure of the exhaust-port diminishes the power of the 
engine to the extent represented by the unnecessary work 
done in compression. This may be enough to lift the valve 
off its seat, which will be shown by a knock or slam when the 
valve opens and it comes down into contact with its seat. 

89. Exhaust-clearance. — It will be apparent that the in- 
side or exhaust lap will make the exhaust sluggish by reason 
of its tendency to contract the exhaust-passage and produce 
the effect called wire-drawing. This danger is most to be 
dreaded in engines of high rotative speed (par. 35); and to 
avoid this difficulty in engines of this class designers have 
sometimes lengthened the hollow in the valve, so that when it 



l68 MECHANICAL ENGINEERING OF POWER PLANTS. 

stands in its central position the distance between the edges 
of the hollow is greater than the distance between the inner 
edges of the steam-ports. The distance which the hollow 
lacks to enable it to meet the inner edge of the port is called 
exhaust-clearance or inside clearance. Its use is restricted to 
high-speed engines and to those in which the expansion by 
means of lap is not carried very far. The difificulty would be 
from the too early release of the expanding steam. Exhaust- 
clearance is sometimes called also exhaust-lead. Its effects 
are to free the exhaust and to diminish back-pressure at the 
bep["innincr of the return-stroke. 



I 



/■ ' 







Fig. 131. 

90. Lead in the Slide-valve — It is often considered 
desirable to have the valve partly open before the piston 
reaches its dead-centre, in order to bring full boiler-pressure 
on the piston at the beginning of its stroke. In other words, 
to have the valve lead the piston. The definition of lead is 
the amount which the steam-port is open when the piston is 
at its dead-centre ready to begin its stroke. Referring to Figs. 
124 and 131, the port-opening between the edge of the valve 
and the edge of the port is the lead. It will be seen at once 
that the lead is a matter of adjustment merely, while the lap 
is a matter of construction of the valve. Lead may be varied, 
but the slide-valve lap cannot. 

It will be apparent that the effect of lead on the setting of 
the valve-crank or eccentric will be to increase still further 
the angular advance of the valve-crank beyond the 90° 
advance discussed in par. 93. The setting 0^ a valve having 
both lap and lead requires that, after the valve has been set in 
its central position with the valve-crank 90° ahead of the 
main crank, the eccentric is to be set forward in the direction 



VALVES AND VALVE-GEARING. 1 69 

in which the engine is to move through an angle whose sine 
is the lap, and then through a further angle whose sine is the 
desired lead. 

91. Effects of Lead. — The effects of sliding the eccentric 
forward in order to give lead at the steam-edges are five. 

1. To increase the angular advance and modify the setting 
adjustment. 

2. To increase the expansive working by causing the 
steam-edge of the valve to close the admission-port by so much 
earlier as the valve has to move before the piston reaches its 
dead-centre in order to give the determined lead. 

3. The effect which these two phenomena have is to in- 
crease the distortion of the exhaust period. The prerelease 
and compression are increased, or the effect of the inside lap 
is neutralized at one end and increased at the other. 

4. The clearance-volume and port passages are filled with 
steam entering the cylinder before the piston reaches its dead- 
centre, so that full boiler-pressure comes on the piston at the 
very beginning. 

5. The living force of the reciprocating parts is arrested 
by this cushion of live steam from the boiler. The effect is 
the same as if it were done by the exhaust-cushion, but it is 
produced by steam which must be paid for instead of by steam 
which would otherwise be wasted. 



CHAPTER VIII. 
VALVE-GEARING, CONTINUED. 

92. Setting of Slide-valve without Access to Valve- 
chest. Setting by Sound. — The slide-valve of an engine 
works in a valve-chest. This is a box either cast in one piece 
with the cylinder and arranged with lids or bonnets by which 
access can be had to the valve and seat, or else the- valve- 
chest is cast separately and secured to the cylinder-casting by 
carefully made steam-tight joints, which are kept tight by 
bolts. The opening of the valve or steam-chest for the pur- 
pose of setting the valve is to be prevented when possible, 
inasmuch as to break a satisfactory steam-joint is a thing 
which is to be avoided. It is by no means difficult to transfer 
the motion of the valve to reference-points outside of the 
valve-chest so as to avoid the necessity for getting into the 
chest. This is easily done by means of a trammel as pre- 
sented in Figs. 127 and 132. 

It will be apparent that if one end of the trammel is placed 
in a centre-punch mark on the valve-chest at such a point as, 
for example, on the stuffing-box, the other end can be used 
to fix upon the valve-stem itself a point which shall indicate 
the position of the valve within. If the engine be turned 
over by hand so that the valve-stem is made to travel to the 
right, the trammel can be made to locate a point on the valve- 
stem in which the outer end of it fits when the valve is all the 
way .over to the right (Fig. 132). If the engine be turned 
over further, so that the valve-stem slides to the left, the 
trammel locates a point on the stem which belongs to the 
extreme of the travel to the left. Half-way between these a 
point can be marked by a centre-punch, and when the point 

170 



VA L VE-GEA RING. 



171 



of the trammel lies in that punch-mark, the valve is in its 
central position. The engine being located with its piston 
upon its dead-centre, the eccentric can be slid around until 
the valve is in its central position, and with the trammel in 
place the valve-stem can be moved through a distance, first, 
to bring the lap line and line with the port edge, and, secondly, 
the further distance proper for the desired lead. As in par. 




Fig. 132. 

83, due regard must be had to direction of motion and to the 
possible reversal of connection by rock-shaft or otherwise. 

Another method of setting the valve without taking off the 
valve-chest lid or bonnet is to depend upon the regular pulsa- 
tions of the exhaust, as they furnish an indication to the ear. 
Their regularity in time indicates a symmetrical motion of the 
valve, and their regularity in intensity or volume indicates 
admission of steam and expansion symmetrically at the two 
ends. This is much the most sensitive method in two-cylin- 
der engines with quartering cranks, as in the locomotive. 

The last appeal as to accuracy of valve-setting is given by 
the steam-engine indicator (Chapter XXX), which should give 
symmetrical and equal diagrams of effort at the two ends of a 
cylinder with valves properly set. 

It will be apparent that it is possible to correct something 
of the irregularity in an unbalanced vertical engine (par. 17) 
by the setting of the valve so as to compensate for the differ- 
ence in effort due to the weight in the reciprocating parts on 
the upward and downward strokes. When the piston-rod is 
of large diameter in a horizontal engine it will subtract a 
measurable area from the surface exposed to pressure. This 



^2 MECHANICAL ENGINEERING OF POWER PLANTS, 



irregularity can be compensated for by valve-setting. In an 
engine having a relatively short connecting-rod more power is 
absorbed in accelerating the reciprocating parts on the stroke 
from the inner dead-centre than is required to accelerate from 
the outer dead-centre. The reason for this is that the con- 
necting-rod compels the piston to move more than half-stroke 
as the crank revolves from o° to 90° on the outgoing stroke, 
and less than half-stroke as it revolves from i8o°to 270° on the 
incoming stroke. As the piston does not have so far to go 
in equal time, it does not have to move so fast in that time. 
It is a minor irregularity, and can be compensated in the valve- 
setting. 

93. Motion-curves for Slide-valves. — A convenient 
method for representing graphically the motion of a slide- 
valve upon its seat was early elaborated by Continental 
engineers and mathematicians. If a line be drawn vertically 
with a length representing, on any convenient scale, the stroke 




Fk;. 133. 
of the piston from one dead-centre to the other, and at points 
of convenient subdivision of this line the distance of the valve 



VALVE-GEARING. 



^73 



from its central position be laid off at right angles to the line 
and upon the same scale, the curve drawn through the ex- 
tremities of the lines which represent the motion of the valve 
will be called a motion-curve, and was early suggested by 
Uhland. If, instead of developing the motion for a stroke and 
back again, the curve be made a continuous one, it becomes 
an ellipsoid. Both offer advantages for graphical use. If, 
instead of one line representing the piston-stroke, six lines be 




Fig. 1-34. 

drawn perpendicularly through the four edges of the steam- 
port and the two edges of the exhaust-port, as in Fig. 133, 
and the valve-section be sketched in its central position, it will 
be easily possible to describe by points the four niotion-curves 
for the effective edges of the valve which will give the curved 
lines shown in Fig. 133. The distances which the valve 
moves from its central position for each horizontal division of 
the vertical line are taken from a circle whose radius is the 
throw of the valve corresponding to the same angular position 
of the valve-crank as is given for the piston of the engine by 
the horizontal lines. Such a motion-curve gives the points 



174 MECHANICAL ENGINEERING OF POWER PLANTS. 

of cut-ofT, exhaust-closure, release, and admission for easy- 
study. By varying the amount of lap in the assumed valve- 
section inside and outside, and by varying the lead, other 
forms of curves which are given in Figs. 134 and 135 result 
from such assumed conditions. It is possible also to observe 




the effect of increasing the throw of the valve, which is the 
change introduced in Fig. 136; its conditions are otherwise as 
in Fig. 135. The effect is to make the cut-off later when the 
throw is increased. These motion-curves can be experimen- 
tally drawn by the engine itself. If a board carrying a 
stretched paper be made to slide by attachment to the cross- 



VA L VE- GEA RING. 



175 



"head, while the bell-crank attached to the valve-stem at one end 
carries a pencil at the other so that the motion of the valve 
is transformed into one at right angles for the pencil, the 
pressing of the pencil against the paper as the engine makes 
a stroke out and back will describe a motion-curve (Fig. 137). 




Fig. 136. 
The motion-curve method, while very convenient for 
studying the peculiarities of valve-motions which have already 
been worked out and for working with cam-motions, is not 
applicable to the design of new valve-gears which must be 
worked out to meet and fill designated conditions. For this 
purpose the method originating with Professor Zeuner is the 
most usual and generally adopted, although modifications 
have been made by several persons. 



170 MECHANICAL ENGINEERING OF POWER PLANTS. 

94. The Zeuner Polar Diagram for Slide-valves. — The 

mathematical basis of the Zeuner diagram represents the 




motion of the valve from its central position, corresponding 
to any crank-angle, by an equation involving the length of the 



VAL VE-GEARING, 



177 



crank and connecting-rod which drives the valve, the length 
of the valve-stem, and the angles which the crank and con- 
necting-rod make with the straight line through the centre of 
motion of the valve-crank. This line coincides with the seat 
of the valve or is parallel to it. When this equation is 
deduced and simplified (seethe Appendix), the second step in 
the demonstration shows that this simplified equation is a 
polar equation, and the distance which the valve has moved 
from its central position for any crank-angle is the length of 
a radius vector swinging around a pole on the circumference 
of a circle whose diameter is the radius of the valve-crank. 
The angle which the diameter of this polar circle makes with 
the line parallel with the valve-seat will be determined by the 
angle which the valve-crank makes with the line through the 
dead-centre when the valve is at its extreme point of throw; 
in which case the radius-vector becomes equal to the diameter. 
If there is neither lap nor lead nor cut-off, and the condition 
is that of Fig. 133, the radius vector should be zero at the 
dead-centre and should have its maximum value at 90'^ 
(see motion-curve, Fig. 133) as in Fig. 138. If the valve has 




a lap, then, at the dead-centre of the piston, the valve should 
be distant from its central position a distance equal to such 
lap, and the radius vector for a horizontal engine, which has 



1/8 MECHANICAL ENGINEERING OF POWER PLANTS. 

been assumed in all this discussion, should have a value equal 
to this lap. This compels the polar circle to occupy a position 
at dead-centre such as represented in Fig. 139. OX repre- 




FiG. 139. 

sents the lap, if the figure is drawn full size. If the engine 
has lead as well as lap, the valve must be distant from its cen- 
tral position a distance equal to the sum of the lap and the 
lead. The radius vector at the dead-centre must then have a 
value represented by Oy when xy is the lead (Fig. 140). 

In these illustrations the engine-crank is to be assumed 
as belonging to a horizontal engine on its inner dead-centre, 
and the rotation to be opposite in direction to that of the hands 
of a clock. The maximum throw is reached when the crank 
of the engine is in the position OB, and beyond this angle the 
valve starts to come back and close the admission. The clos- 
ure of admission will occur when the valve on its return towards 
its central position is distant from it a length equal to the lap 
(pars. 85 and 86); hence if with (9 as a centre and with Ox 
as a radius a circle be drawn, it will intersect the circle whose 
diameter OB equals the throw, and v/hich is called the valve- 
circle, at points which will indicate the angles at which the 
valve begins to open and at which it closes. The radius 
drawn through Z (Fig. 140) gives the crank-angle at which 
the inlet-valve opens, and a radius drawn through J'F gives the 



VA L VE-GEA RING. 



179 



crank-angle at which admission ceases or the cut-off takes 
place. It is obvious that in a valve with lead the valve would 
open before the piston reaches its dead-centre. 

A strict adherence to the Zeuner method would have the 
circle described on OB conceived as attached to the engine- 
shaft, and the crank when at its dead-centre to lie in the 
position ON. It is so much easier to cause the radius to 
swing through equal angles in the contrary direction, while 
the valve-circle remains fixed, that this method is preferred 
for practical use. 

If the diameter BO be produced beyond O to C, and a 
second circle of equal diameter be drawn upon (9(7 as such 
diameter, a circle is given whose radius vectors give the 

B 




Fig. 140. 

■exhaust events. If there is no inside lap, the exhaust opens 
and shuts when the radius vector of this second circle is zero, 
which is the position when the crank is at (9/^and OQ (Fig. 143) 
If there is an inside lap, the port will not open until the valve 
has moved through that lap. Hence the effective opening 
will begin only when the radius vector for the secondary circle 
exceeds the lap. Therefore if with (9 as a centre and inside 
lap Or as a radius a circle be drawn, its intersections with the 
secondary circle will give the crank-angle at which the exhaust 
on the working stroke and compression on the exhaust-stroke 
begin. 



l8o MECHANICAL ENGINEERING OF POWER PLANTS. 

95. Use of the Zeuner Polar Diagram. — The Zeuner 
polar diagram not only gives all information which \?> given by 
the motion-curve, but it furthermore enables the user to design 
the valve and seat to fulfil specified conditions. In Fig. 140 
the throw lap and lead are the given data. The angle AOB 
shows the advance of the eccentric disk beyond 90° proper 
for such lap and lead, and the cut-off takes place at an angle 
AOP ixowi the beginning of the stroke at dead-centre. The 
design of a valve and its seat proper for the conditions 
assumed will give a drawing such as Fig. 141. 

It is desirable that the valve in sliding upon its seat should 
come to the edge of it in its extreme throw, in order that the 
wear of the valve and seat may be uniform all over their 




Fig. 141. 

surfaces of contact. Starting, therefore, at the point (9, which 
marks the extreme edge of the seat, a distance OB is laid off 
equal to the throw OB (Fig. 1 40), which is the radius of the 
valve-crank, and the maximum distance it can throw from its 
central position. The point B will be the beginning of the 
valve, since it projects over the port a distance Ox equal to 
BW 3.nd equal to the lap, and consequently at the point Z in 
Fig. 141 the outer edge of the port should begin. With the 
assumed throw of the valve and the assumed lap the port can 
never be opened wider than the distance 7'B in Fig. 140. 
Hence the indicated size for the port IVPj Fig. 141, is the 
length vB in Fig. 140. If the port were made larger, the 
throw chosen would not open it w^ide, since BP equals OB; 
and if JVP w^ere less than 7'B, the valve in sliding would go 
beyond the point P, w^hich is unnecessary. The calculation 



VA L VE-GEA RING. 1 8 1 

or design must be checked at this point to ascertain whether 
the area of the port-opening given by the product of WP mul- 
tiplied by the permissible length in the direction perpendicular 
to J^F/* giv^es an area sufficient or unnecessarily large to admit 
the quantity of steam required in the cylinder per stroke ac- 
cording to the calculation made in par. 8i. 

A valve having no inside lap will have the inner edge 
of its working face which is the beginning of the exhaust- 
hollow line and line with the edge W ol the port. If there 
is an inside lap, represented by Ov in Fig. 140, it will give a 
projection of the valve-face beyond the port-edge P. 

The steam-port must be separated from the exhaust-port 
by a partition. The a-mount of metal in this partition is 
immaterial provided only it is enough to secure stiffness. It 
is often one half the port width PW or vB^ when there is no 
reason for making it anything else. The only effect of metal 
in this bridge or partition is to lengthen the valve and increase 
the power required to slide it on its seat (par. 81). 

The inner edge of the exhaust-hollow travels to the right 
or left a distance equal to OB, or the throw of the valve. It 
is desirable that when it is moved all the way to the right the 
hollow face shall still leave between its edge and the point or 
line V a space TV, equal to or larger than the port PW, 
discharging into that hollow from the right-hand port. That 
is, the motion of the valve to /^should not constrict or reduce 
the passage through which the exhaust is escaping any further 
than it is necessarily reduced by the fixed opening correspond- 
ing to PW. This fixes the right-hand edge of the exhaust- 
port in the seat, and the rest of the valve and seat is made 
symmetrical with the left hand half already constructed. 

96. Valve-gear Problems and Design. — It is outside 
of the present purpose to follow the use of the Zeuner valve- 
diagram further. It can be made to solve problems covering 
all quantities when a few assumptions or data are made or 
given. The point of cut-off is one of the most usual aata, as 
the engineer in most cases desires to work his steam with a 
certain expansion. The lead is another fundamental assump- 



1 82 MECHANICAL ENGINEERING' OF POWER PLANTS. 

tion. But a variety of combinations is possible involving the 
throw of the valve, the port-opening for a certain position of 
the crank, the release and the compression ; and for these the 
student is referred to special treatises. 

For the immediate purpose in hand, however, the special 
problem will be considered in which the throw, point of cut- 
off, and lead are given and it is required to find the angular 
advance and lap to fill the condition assumed. 

In Fig. 142 let the horizontal line AB reoresent the 




Fig. 142. 

whole travel of the valve in a horizontal engine. Bisect the 
line at O and with OA as radius describe a circle on AB as 
diameter. Draw the radius OC^ representing the angle from 
B as dead-centre at which it is proposed to have the cut-off 
take place. This is the point of closure of the valve; and 
since there is to be a lead, the valve should open before the 
crank reaches the position OB. The amount of angular 
motion before the crank reaches OB should be that through 
which the centre of the crank should move in subtending an 
angle measured by that lead. If, therefore, with ^ as a centre 
and the radius Bl, equal to the assumed lead, a circle be 
drawn, the radius OD will give the position at which the valve- 
crank stands when the port just begins to open. The maxi- 
mum radius vector will be at a point half-way between these 



1 



VAL VE-GEARING. 



185 



two crank-positions OD and OC, so that if the. angle DOC is 
bisected by any of the usual geometric methods and the 
position OE thus determined, the angle HOE will be the 
angular advance ahead of 90° at which the valve-crank should 
stand. The length OX cwt off from the line OC by the valve- 
circle just drawn is the vaiue of the radius vector, or distance 
of the valve from its central position, when the steam-edge 
coming back over the port cuts off admission. OX is there- 
fore the value of the lap, and a circle drawn with O as centre 
and 6^X as radius will be the lap-circle for that diagram. It 
is a matter of simple geometric proof to show by similar 
triangles that the length yz, which represents the lead in its 
customary position, is the same as the length Bl used as an 
expedient in construction. 

97. Limitations of the Single Slide-valve. — The cheap- 
ness, convenience, simplicity, and permanency of the single 
slide-valve are the great inducements to its use. It can be 
shown, however, by the method pursued in par. 96 that the 
limit of expansive working with a single valve performing all 




Fig, 143. 

functions is reached before it is demanded to cut off at 
half-stroke. If the conditions of cut-off at half-stroke be im- 
posed and the method of par. 96 be followed, it must be 
apparent from Fig. 143 that the angle HOE will be a little 
greater than 45° if there is a lead, and will be 45° if there is 



1 84 MECHANICAL ENGINEERING OF POWER PLANTS, 

none. The drawing of the circle of the lap with a radius OX 
determined by that valve-circle will give a lap so large in 
relation to the throw OH that the port-opening becomes 
absurdly small. 

The matter is not materially helped by increasing the 
throw, because the lap increases with the throw. 

Furthermore, if there is no inside lap, the exhaust-opening 
and closure will take place at angles represented by the lines 
OP and OQ, which, it will be seen, are 45° from the crank- 
position which belongs to the ends of the stroke. The 
exhaust events have thus become distorted so that successful 
working becomes impossible. Hence with high expansion, 
secured by the expedient of increasing the angular advance of 
the valve-crank, the limit is certainly reached before two 
expansions are secured. A much higher degree of expansion 
is desired in all fly-wheel engines. How shall it be secured ? 

98. Valve-gear for High Degrees of Expansion. Two- 
valve Systems. — The advantages of the single valve induce 
an effort to make use of it if possible. Particularly in such 
mechanisms as that of the locomotive and the marine engine, 
where complication is to be avoided, it is desirable to retain 
the single slide. 

(i) The first method is to design the engine or its gear 
so that, as it is desired to cut off earlier, the throw of the 
valve should be lessened. It will be apparent that if the 
throw were equal to the lap or less than it, the valve would 
not move from its central position far enough to uncover 
either port. This makes the cut-off before the stroke begins, 
and is the limit. If a port of extra width or length will give 
area sufficient to let steam through in sufficient quantities to 
give the engine the necessary power, the admission will stop 
earlier and earlier as the throw diminishes, but, the angular 
advance remaining constant, the exhaust-ports open and close 
at the required angle for which they were designed. This 
principle underlies many designs of automatic cut-off engines, 
in which the governor varies the throw of the valve as the 



VA L VE-CEA RING. 



185 



speed varies. It is also one of the underlying features of the 
link-motion used as a cut-off gear on locomotives. 

(2) The second method to secure high expansion is to use 
two slide-valves. These may work in the same valve-chest 
or in different valve-chests. When the two valves work in 
the same valve-chest it is usual to have them operated by 
separate eccentrics, and to divide the functions of distribution 
between them. The valve nearest the seat Avill control the 
exhaust-port openings entirely, and will be driven by an 
eccentric having a comparatively small angular advance. This 
principal valve will be called the main, or distribution, valve. 



fc-Z.--!. 




Fig. 144. 

The second valve will be driven by its own eccentric, set at a 
considerable angular advance, and will have no exhaust func- 
tions. Its business will be solely to cut off admission of 
steam into the ports or passages through the main valve 
whereby steam is admitted to the ports in the seat (Fig. 144). 
This valve will be called the cut-off valve, and from the fact 



1 86 MECHANICAL ENGINEERING OF FOWER PLANTS. 



that it slides or rides in the back of the main valve this 
arrangement is often called the riding cut-off. The main 
valve requires to be prolonged so as to form the seat and port 
for the cut-off valve. The inner edge of this port performs 
cut-off functions late in the stroke, and prevents the cut-off 
valve from opening by its return motion the port which its 
greater angular advance has caused it to close. This riding 
cut-off arrangement lends itself easily to automatic adjust- 
ment of cut-off, since the release and compression are provided 
for at fixed points by the lower or main valve, and admission 
can be varied within very wide limits without affecting these 
exhaust functions. It may be a solid block, or in two sep- 
arate blocks adjustable on their rod, as in the type of Meyer 
valve selected in Fig. 144. 

A modification of this system has a partition between 
the two valves, with one or two rectangular openings in it (Fig. 




riG. 145. 



145). Steam from the boiler passes to the main valve below 
the partition when the cut-off valve uncovers the opening. 
The objection to this arrangement is that the steam which 
surrounds the main valve partakes of the expansion after the 
admission is cut off by the upper valve, and the work of such 
expanding steam is lost. In the riding cut-off to diminish 
this loss as far as possible, the thickness or height of the main 
valve is kept as small as consistent with giving the exhaust- 
hollow the depth which it requires. The small port /^ is a hand 
opening, or by-pass, to let steam enter the main valve-chest if 
the engine shall have stopped with the upper port closed. 



VA L VE- GEA RING. 



187 



When two valves are used in separate chests, the exhaust 
functions belong to one and the steam functions to the other. 
This makes both design and variation of cut-off exceedingly 
simple. Fig. 146, showing a section of the Porter-Allen 



g£lL rCThM 




engine, presents the features of a valve-gear of this sort in 
which the two valve-chests are on opposite sides of the 
cylinder and both are slide-valves. It will be easily seen 



1 88 MECHANICAL ENGINEERING OF POWER PLANTS. 

from pars. 94 to 96 that the steam-valve need be planned 
only for lead, lap, and throw, and the exhaust-valve for throw 
and lap, when compression and release are fixed. 

99. Three- and Four-valve Gears. — When the principle 
of one valve has been abandoned it becomes very simple to 
design valve-gearing with a steam-valve for each end and 
an exhaust-valve for both ends, making a three- valve engine, 
or a separate valve for steam and exhaust at each end, making 
the four-valve engine. In both the three- and the four-valve 
engine the same advantages are derived, having the com- 
pression and release occur at fixed points in the stroke, while 
the cut-off and expansion can be varied automatically or by 
hand without interfering with the exhaust functions. The 
forms taken by the three- and four-valve systems present 
almost every combination of lifting- and sliding-valves which 
can be made. The typical river-boat engine, the older blow- 
ing-engines, and the older beam-pumping engines illustrate 
types of lifting-valves, and the Corliss engine and its imitators 
illustrate the cylindrical sliding-valve to accomplish these 
same results. Before examining these mechanisms in detail 
it is desirable to discuss some special features. 



CHAPTER IX. 

VALVE-GEARING, CONTINUED. 

100. Shortening Steam-passages. — In the typical sh'de- 
valve which has been discussed hitherto the valve has been 
considered as short as consistent with adequate area for ports 
and for the exhaust-hollow. This results in engines of long 
stroke in a considerable length from the port at the valve-seat 
to the end of the cylinder. As a rule in this design the valve 
is in the middle of the length of the cylinder, although this is 
not necessary if it be more convenient to have one passage 
longer than the other. The objections to the long passages 
from the valve-seat are: 

1. The friction which they oppose to the passage of the 
steam. These passages are usually moulded in the cylinder- 
casting by means of cores of proper shape, and their surfaces 
will be rough. The effect of this friction is to increase the 
difference of pressure which exists in the boiler or valve-chest 
and in the cylinder. 

2. The long passage cools the steam by contact with its 
sides. This cooling is first by ordinary radiation, but more 
important than this is the cooling which follows when the 
passage is in communication with the exhaust-port. The 
lower-pressure steam, carrying perhaps a mist of watery par- 
ticles, will absorb heat very rapidly during that part of the 
stroke in which it is serving as an exhaust-passage. The 
longer the surface the more heat will be required from the 
entering steam on the next stroke to heat the metal up to the 
temperature of the entering steam. 

As has been heretofore observed, there is no difficulty in 
lengthening the valve and thereby shortening the passage. 

189 



1 90 MECHANICAL ENGINEERING OF POWER PLANTS. 

The size of the exhaust-hollow and the bridges which separate 
the ports produce no effect upon the distribution. The only 
objection is that increased length of valve gives an increased 
area for pressure, and consequently makes the valve demand 
more power to move it. In early designs for low-pressure 
steam, where this matter was of little moment, engines with 
very long slide-valves will be found. They have been some- 
times called Murdoch's valves. With high-pressure steam the 
difficulty has been met in another way. When the single 
eccentric is to drive a valve performing all valve-functions the 
usual plan is presented in Fig. 147. It will be observed that 




Fig. 147. 



while the valve acts as one it is really made in two parts, or 
like a B valve. The exhaust-port is divided by its special 
bridge, and the admission of steam is controlled by the left- 
hand edge of the left half of the valve and by the right edge 
of the right'hand half. The length of passage is thrown into 
the exhaust, where it makes no difference, and the length 
of the steam-port at each end is reduced to the shortest possi- 
ble line. By joining the two halves by a rod surrounded by 
the steam in the chest there is no pressure on the valve 
between the active parts at each end. This same result is 
sometimes attained by making the valve resemble a low and 
broad letter H in plan. The uprights of the H are the work- 
ing-parts of the valve, and the cross-bar between is made 
hollow and fits the exhaust-port, whose length is at right 
angles to the length of the steam-ports (Fig. 148). 



VAL VE-GEARING. 



191 



lOi. Shortening the Throw of the Valve. Allen Valve. 

— Another expedient for diminishing the power absorbed by 
an engine in working its own valves has been to shorten the 
throw or travel of the valve upon its seat. This raust be 
done without constricting the port-area, which is an essential 




Fig. 148. 

condition. If by keeping the throw of the eccentric larger 
than the throw of the valve, there is yet opened an equal 
port-area with such reduced throw, there has been given to 
the eccentric a mechanical advantage to overcome the pressure 
which holds the valve at its seat. Fig. 149 shows the Allen 
slide-valve whose characteristic is the passage or hollow 
through the shell over the exhaust-port, and the use of a com- 
paratively short seat or a seat with more than three ports in 
it. From the construction and the proportions it will be seen 



192 MECHANICAL ENGINEERING OF POWER PLANTS. 

that when the steam-edge of the valve uncovers the left-hand 
port by a motion of the valve from its central position the 
hollow in the shell is by that same motion brought into com- 
munication with the steam-pressure at the other end of the 
valve. In consequence of this a given motion opens twice as 




Fig. 149. 

much port for the passage of steam into the cylinder as would 
be the case in the ordinary valve. Steam-pressure is thus 
very rapidly established as the valve moves a less distance 
than the port width which it is made to serve. 

102. Gridiron Slide-valve. — It will be immediately ap- 
parent that if the slide-valve be constructed with alternate 
holes and solid bars each of one inch in width which match 
similar holes and bars in the seat, that the motion of one inch 
which brings the holes in the valve to match the holes in the 
seat will open an area of port as many times one inch in the 
direction of motion as there are holes in either valve or seat. 
Fig. 160 shows a slide-valve of this construction, intended for 
steam only. It is called from its resemblance a gridiron 
slide-valve, and the principle of having many openings into 



VA L VE- GEA RING. 



193 



the steam-passage gives it also the name of multiported valve. 
The adoption of this principle will be observed in many large 
engines, and is particularly useful for high pressures. 

The multiported valve-seat can also be made to serve 
another purpose, which will be understood from Fig. 161. 



Fig. 160. 




Fig. 161. 

The division in the port is carried all the way down to the 
bore, so that the piston in its movement towards the head of 
the cylinder closes the inner port at either side before it 
reaches the end of the stroke. This inner port has been the 
principal dependence as an exhaust-port, so that when it is 
closed by the piston a very energetic compression is the result, 
atxd the piston is arrested by a cushion of the exhaust-steam. 
On the steam end the admission is gradually cut off by the 
closure first of one port and then of the other. This principle 
of using the piston as a valve to close ports in the bore of the 
cylinder is the principle underlying several designs of so-called 
valveless engines. A modification of it is to be noted in Fig. 
65. 

103. Balancing Slide-valves. Piston-valves. — The power 
necessary to slide a valve upon its seat is measured by the 
area of the valve multiplied by the pressure upon that area,^ 



194 MECHANICAL ENGINEERING OF POWER PLANTS. 

and by a factor expressing the coefficient of friction between 
the valve and its seat. The pressure is the net pressure or 
the algebraic sum of the downward pressure on the valve and 
the upward pressure exerted from the cylinder against the 
under side of the valve. It is not a difficult matter to make 
this calculation for assumed conditions (see Appendix). The 
work in foot-pounds per minute to slide the valve upon its 
seat will be the product of the previous factors multiplied by 
the feet per minute through which this resistance to motion 
is overcome. It will be seen that the previous discussions 
have shown how these pressures may be kept as small as 
possible and how the motion or travel can be diminished. 
With high pressures and large volumes of cylinders to be 
filled steps must be taken to diminish pressure on the valve, 
since the feet of travel must remain always a considerable 
quantity. The most satisfactory method for accomplishing 
this result gives rise to what are called balanced valves. 

The simplest form of balance-valve is what is called the 
piston-valve, which is shown in the section of the valve and 
chest in Fig. 162. The piston- valve consists of an ordinary 
shell or D valve, which has been made to revolve around its 
valve-stem as a centre so as to generate a volume of revolu- 
tion. The plane faces of the typical slide-valve become the 
surfaces of a cylinder, and the plane valve-seat must become 
a hollow cylinder which the vaJve-faces fit like a piston. By 
referring to Fig. 162, it will be apparent that steam-pressure 
is equalized upon the two end-faces of the cylindrical valve, 
and the contact of the valve with its bore prevents any pres- 
sure other than friction from getting at the valve sidewise. 
The only resistance to the motion of such a valve is its own 
friction, no matter how great the steam-pressure may be. 
The valve may be arranged with double pistons as in Fig. 
162, or with single pistons as in Fig. 163. The objections 
to the piston-valve are the difficulties from leakage and wear. 
The pistons cannot fit tight in their bore, because unequal 
expansion would cause them to be seized by the bore when 
the latter was cold and the pistons were hot. To prevent 



VA L VE-GEA RING. 



^95 



excessive leakage they must therefore be made steam-tight, 
by means of spring-rings whose elasticity causes them to spring 
out against the bore while they fit grooves in the piston 
tightly enough to prevent leakage around them. These 
spring-rings must be prevented from catching in the ports 
over which they slide by bridges of metal which prevent 
their enlargement when the rings are opposite the ports. 




Fig. 162. 
These rings, nowever, cause friction and wear. When the 
piston-valve is used without rings great care must be taken to 
prevent the possibility of difference of temperature between 
the piston and its bore. Unequal expansion would cause the 
piston to be cramped by the bore, and this must be prevented 
by jacketing the latter with extreme care. Fig. 162 shows 
this precaution taken. The piston-valve precludes great re- 



IQO MECHANICAL ENGINEERING OF POWER PLANTS. 

duction of the clearances and the shortening of the passages. 
For very large marine engines, in order to diminish the 
diameter of the valves and at the same time to shorten, 
certain connections, two sets of piston-valves are used, work- 
ing together from a common valve-rod. The piston-valve is 
extensively used on steam-hammers, rock-drills, and the like. 
Its great advantage for steam-hammer practice in large sizes 
comes from the ease with which the valve can be worked b}^ 




Fig. 163. 

hand. A favorite form for such piston-valves is rectangular 
or square instead of round. Round pistons are easier ta 
make and to pack. 

104. Pressure-plate Systems. — The pressure-plate sys- 
tem aims to secure the release of the valve from unbalanced 
steam-pressure by receiving that pressure on a plate which is 
supported positively in the steam-chest and underneath which 
the valve shall slide. The principle is fundamentally the 
same as the piston-valve; but the valve can be flat, and need 
only be steam-tight on its top and bottom, where it touches 
the seat and pressure-plates, respectively. 



VA L VE- GEA RING. 



197 



There are three great systems of arranging the pressure- 
plate principle. First, the fixed plate, non-adjustable. In 
this design the fixed plate rests upon lugs or ledges in the 
sides of the steam-chest, or on its bottom, the length of the 
plate being such that the valve will always remain under it as 
it travels (Fig. 159); or the plate may be the top of the 
steam-chest. The valve may have no packing provision as in 
I^'ig' I59> <^r an adjustment may be provided as follows: To 




Fig. 159. 

the back or top of the valve is fitted a spring-ring or an 
equivalent device, which fits the valve and the plate in such 
a way that no steam can reach the top of the valve by reason 
of the contact continuously made between the valve and the 
plate through the spring-ring. It will thus be seen that the 
valve is in equilibrium of steam-pressures all around it except 
on its back, and the only resistance to its motion is the fric- 
tion caused by the elasticity of the packing device. It is 
frequently arranged to have the space inclosed by the pack- 



198 MECHANICAL ENGINEERING OF POWER PLANTS. 

ing-ring communicate with the exhaust through a hole, so 
that if the packing-ring should leak, the leakage would be 
into the exhaust-pipe, and it would be impossible for pressure 
to get upon the valve. Fig. 164 shows the balanced valve 
of this fixed pressure-plate and adjustable-ring type. The 
design chosen for exhibition is one which has been much used 
in locomotive service. In Fig. 159 the pressure-plate has 
relief-valves on its back which can open by excess of pressure 
from below, due to water forced back from the cylinder 
through the extra length of the ports. The piston-valve and 




Fig. 164, 



the inelastic pressure-plate do not allow this displacement of 
the valve by excess of upward pressure. 

The second type of pressure-plate systems is shown in 
Fig. 165. In this design the valve is a solid block, but the 
pressure-plate which fits upon its back is arranged to be sup- 
ported upon an inclined plane. The pressure-plate is also 
made to slope at the same angle, so that by means of the 
adjusting-screw the inclined planes are made to slide over each 
other; the surface which bears on the valve remains always 
parallel to itself. It will be apparent that any desired pres- 
sure of contact can be made between the sliding-valve and the 
pressure-plate while the pressure of steam is kept from the 
back of the valve. The type selected will also serve to illus- 
trate another form of double-ported design for the admission 
of steam through large areas by small motion of the valve (see 
pars. loi and 102). This same method is further illustrated 



VA L VE-CEA RING. 



199 




200 MECHANICAL ENGINEERING OF POWER PLANTS. 

in Fig. 166, where the pressure-plate adjusts across the path 
of the valve by similar inclined surfaces. The same engine 
is shown in Fig. 146. Or, again, the pressure-plate may bear 
upon flat surfaces, from which it is held away by packing- 




'''IfaliiiliM 



Fig. 166. 



strips, which are taken away as wear may render this course 
necessary (Fig. 167). 

The third pressure-plate system has been adopted foi 
rougher grades of work than the two preceding. The pres- 
sure-plate is a disk or plate of steel or similar flexible and 
resilient metal. It is so calculated that the pressure upon it 
shall force it down upon the valve which slides under it, but 
its resistance to such flexure shall be sufficient to permit only 
the desired nip or squeeze to reach the valve and prevent 
leakage of pressure between the valve and the plate (Fig. 
168). In some old designs this flexible pressure-plate was 
supported at its central point by a stud which came up 
through the top of the steam-chest, and could be adjusted 
from outside with steam upon the valve within. 

The first two systems are the most usual. 



VALVE-GEARING. 



20 1 



105. Valves taking Steam Internally. — Closely resem- 
bling the piston-valve and pressure-plate modifications of it 
is the third type of balanced valves. In these provision is 
made to have the upward pressure exerted by the steam upon 

the area made just 
enough less than the 
area exposed to down- 
ward pressure so as 
not to lift the valve. 
The unbalanced force 
tends to keep the valve 
upon its seat. This 
compels the use of a 
hollow valve whose up- 
per side shall either fit 





Fig. 167. 



Fig. 168. 



against a surface, adjustable or fixed, which shall serve to 
keep pressure away from the outside of the hollow valve on 
the side corresponding and opposite to its seat, or a scheme 
is used in which the pressure is balanced around it (Fig. 169). 
These types run naturally into the pressure-plate system with 
steam on the ends only. 

106. Valves with Counter-pressure. — A very simple ar- 
rangement of counterbalances was applied to many Worthing- 
ton pumping-engines of large size. The valve was attached 



202 MECHANICAL ENGINEERING OF POWER PLANTS. 

by a link and pin-joints to a piston. This piston fitted a 
vertical cylinder directly over the valve, the area of the piston 
being so calculated that it was not quite enough to lift the 
valve even when the latter had its maximum pressure under- 
neath it. The cylinder needs only to be long enough to 
permit the swing-link to follow the valve as it moves back 




Fig. 169. 

and forth. This principle of counterpoising pressure by 
means of a piston has also been used in massive vertical 
engines to provide for the weight of the valves and their rods 
and to keep the strain always in one direction. It can also 
be similarly used to counterbalance the weight of the mech- 
anism of the engine itself. 

Locomotives have been fitted with a nest of rollers which 
lie in a groove below the surface on each side of the valve. 
They come just to the level of the seat, and carry the down- 
ward pressure to a degree without allowing leakage below the 
valve and between it and its seat. They form a roller-bearing. 

107. Poppet-valves. — It is one of the great advantages 
of the double-seated lifting-valves that they are nearly, if not 
entirely, balanced. The poppet-valve as usually constructed 
consists of two disks secured to one stem. These disks are 
usually segments of cones so as to seat steam-tight in corre- 
sponding conical holes (Fig. 170). The pressure can be 
broup^ht either between the two disks so as to be downward 



rALVE-GEARING. 



203 



upon the lower disk and upward upon the upper, or the 
pressure may be brought outside of both disks so as to be 
upwards upon the lower and downwards upon the upper. 
It will be apparent, therefore, that valves so constructed can 
be made either perfectly balanced, underbalanced, or. over- 
balanced, according to the area and the direction of the 
pressure. They are most frequently slightly underbalanc9d 
in river-boat engines, where they are much used, because it 
is convenient to construct the valve-seat of the upper valve 
large enough so that the lower valve \\\\\ pass through it. 




Fig. 170. 

This means that the small base of the cone in the upper seat 
shall be just larger than the large base of the disk which 
closes the opening in the lower seat. Balanced lifting-valves 
of this class open a comparatively large area for the passage 
of steam, and have no friction except that of the stems which 
pass out of the steam-chest through the stufBng-box. It 
is doubtless the rise of these stems as the valve is lifted in 
vertical engines, like the appearances of puppets in the old- 
fashioned peep-show, which has given its name to this form 
of valve. 

The objections to it, as applied to vertical engines, are 
the excessive clearance-volume which is entailed, and the 
difficulty of making them so that they will not leak. In 
horizontal engines, where the poppet-valves can lift at right 
angles to the diameter of the cylinder, the loss from clearance 
need not be so great (Fig. 173). 



CHAPTER X. 

CAM AND RELEASE VALVE-GEAR. 

lo8. Cam Valve-gears — The convenience of a cam as a 
means to operate the valv^e distributing steam to the engine- 
cylinder was early appreciated. The profile of the cam, 
whether revolving continuously or vibrating through an arc 
or a part of a circle, can be designed to give to the valve 
exactly the desired motions and at the desired times. It can, 
moreover, hold the valve open or shut while continuous 
motion of other elements or organs is in progress which the 
crank-motion does not permit; and furthermore it permits the 
sudden or rapid closure of the valve by gravity or by a spring 
when the profile of the cam lets go of the stem. 

Cam-motions are of two great classes. In the first the. 

cam-shaft revolves continuously in one direction. In the 

second the cam-shaft is a rock-shaft vibrating through an 

angle first in one direction and then in the other. In cam 

f| valve-gears of the first class there are two 

Jm arrangements usual. In the first arrange- 

J L ment the cam bears against a roller in con- 

^^J^^ ^ tact with its exterior surface; such are called 

E^^''^^^^^^^^^\ outside cams (Fig. 171). The roller is con- 

^pg: y—^' ^^ veniently mounted in the end of the valve- 

^pS V^ ] stem and can be in the plane of such valve- 

>y^ /^ / stem, or the cam may bear against the end 

^"^^^^ ^ of a pivoted lever which actuates the stem 
iG. 171. (Fig. 176). In the other arrangement the 

roller fits in a groove in the side of a cam-plate. 

The outside cam-motion works the valve in one direction 
only; for the return motion ei»ther gravity or a spring must be 

204 



CAM AND /RELEASE VALVE-GEAR. 



20c; 



depended on, or else there must be a roller or yoke opposite 
to the first one to bring the rod back with a motion similar 




Fig. 172. 

to that caused by the cam against the first roller. This out- 
side cam arrangement has the advantage that the roller 
always turns in the same direction. The two-roller or yoke 




Fig. 173. 
plan has a grave objection from the difficulty that wear pre- 
vents the distance between the roller or yoke surfaces remain- 
ing always the same as the net diameter of the cam at every 
point. If the roller or yoke does not touch the cam con- 
tinuously, there is a jar and shock followed by wear at the 
points where such contact begins. 



206 MECHANICAL ENGINEERING OF POWER PLANTS. 



The side-cam arrangement where the roller fits in a groove 
has the entire motion of the valve effected by that one roller 




D 



Fig. 174. 
and- groove. The difficulty is that the inside surface of the 
groove drives the roller on the lifting stroke, and the outside 
surface of the groove drives the roller on the reverse stroke. 




Fig. 175. 

Hence at each reversal of motion the rotation of the roller 
must be instantly reversed, and the inertia of the roller resist- 
ing this reversal prevents perfect rolling contact at those 



CAM AND RELEASE VALVE-GEAR. 20/ 

points of reversal, and wear and rattle ensue. The difficulties 
from the inertia of the rollers and the mass of the valve-rods 
have limited in the past the use of cams to relatively low 
rotative speeds. Recently a design has been brought forward 
in which the reverse motion of the valve-stem is caused by a 
pressure of air or steam upon a piston on the rod, so that 
the mass to be moved by the cam is reduced to its lowest 
terms, and the pressure on all pin-joints is kept constantly in 
one direction (Fig. 176). 

When the cam rocks or vibrates upon an oscillating shaft 
instead of revolving continuously it drives in one direction 
only, and the weight of the rod or a spring, or both, must be 
used to return the valve. This rocking or oscillating cam is 
almost a distinctive peculiarity of the beam-engines used in 
deep-river-boat practice of Eastern America (Fig. 30). These 
are four-valve engines, the two exhaust-valves being on the 
right-hand side and the two steam-valves on the left, as the 
observer faces the engine. Eccentrics on the water-wheel 
shaft transmit a reciprocating motion to cranks upon a rock- 
shaft which crosses the front of the engine and is divided into 
two sections at the middle bearing. The valve-rods are 
lifted by the profiles of curved cams or wipers which bear 
against the horizontal surfaces of toes which are lifted by the 
rocking of the rock-shaft. The exhaust-valves must be open 
full stroke, and consequently the plane of the two wipers has 
almost a common tangent at the dead-centres, so that the 
cam on one side will have just closed the valve at the upper 
end of the cylinder when the cam on the other is to open the 
valve at the lower end. The steam-cams make an angle with 
each other, so that there will be an interval between the clos- 
ing of one and the opening of. the valve at the other end. 
This gives the interval for expansion at the end of each 
stroke, while securing admission at the proper point. The 
eccentric of the steam end of the rock-shaft is usually of 
greater throw than the exhaust side, so as to give greater 
amplitude to the motion of the cams, and the steam-cams are 
made longer than the exhaust-cams, in order to give gentle 



208 MECHANICAL ENGINEERING OF POWER PLANTS. 



curves for their action, and yet open the valves quickly and 
close them promptly. This valve-motion of wipers and toes 




m 



Fig. 176. 
was first proposed by the Messrs. Stevens in 1848, and is 
usually known as the Stevens cut-off. 

The rocking cam also appears in Fig. 173, for actuating 



CAM AND RELEASE VALVE-GEAR. 



209 



the valves of inclined cylinders by bearing against the under 

side of a pivoted lever to which the poppet-valve is attached. 

The Western river-steamboat with horizontal engines for 




its water-wheel usually operates its valves by continuously 
moving cams on the water-wheel shaft, which bear against 
the surfaces in a frame to which the revolving rod is attached. 
The relatively slow motion gives rise to no difficulty with this 
type of gear (Fig. 172). 

Cam motions can be made adjustable or variable by 
arranging to have the profile of the cam variable. This 



2IO MECHANICAL ENGINEERING OF POWER PLANTS. 

is usually done by having the cam made up of several layers 
which are movable over each other in such a way that the 
acting face of the cam can be made shorter or longer at the 
pleasure of the operator. Or the cam is made of a varying 
profile at different sections of its considerable face, and dif- 
ferent parts are brought under the roller or valve-lever (Fig. 

174). _ 

It is not often attempted in cam valve-gears to make one 
cam and one valve perform all the valve-functions. Cam valve- 
gears are usually three- or four-valve designs. The cam gear 
is usually worked with poppet-valves, because the valve must 
oppose the least resistance to motion, and must be balanced 
so as to be self-closing. Examples of cam valve-gear will be 
found in Figs. 172 and 173. Fig. 175 shows an arrangement 
which holds the valve open or shut through a considerable 
angle of the rotation of the shaft. 

109. Trip or Releasing Valve-gears. — Belonging to the 
same general class as the cam gears are those in which a 
detent or catch which is pushed or pulled to open the valve is 
released when the valve is to be closed, so that it returns to 
its closed position independent of the operating mechanism. 
This return is effected usually by a weight or a spring or both, 
so that the valve is closed more quickly than it could be if the 
connection of the valve to tfie operating mechanism were posi- 
tive. This principle of trip or release gears is identified in 
America with the name of Frederick E. Sickles (1841), but 
has received its greatest development under the name of Corliss 
(1849), with whose name it is best identified in Europe. 
The original Sickles cut-off was applied to poppet-valves 
lifted by cams. When the cam had lifted the valve-stem to 
the desired point, a latch connection between the stem and 
the lifting mechanism was released and the valve closed inde- 
pendently b}^ dropping. As the lifting mechanism descended 
it displaced the latch or detent until it had passed the latter, 
when, by a spring, the latch came forward into position to be 
caught by the lifting mechanism when it was to make its next 
stroke. As applied to early engines the Sickles principle 



CAM AND RELEASE VALVE-GEAR. 



211 



was arranged to have the latch release adjustable by hand. It 
becomes easy to have this adjustment made automatically 
by the governor, and this easy adaptation has been a great 
stimulus for the development of this class of valve-gear. 
A type of gear v^hich presents the trip-and-release mechanism 
in its simplest form is that which is identified with the Greene 
engine, Fig. i8o. It will be seen that the slide y traverses 

m 




T3J i 

Fig. i8o. 
back and forth driven by an eccentric. This slide carries the 
latches GG, which are held upwards by means of springs and 
are inclined upon their upper faces. It will be apparent that 
as the sharp corner of the latch catches the end of the arm B 
it will swing it upon one stroke, but will be depressed by it 
on the other. As soon as it has passed by,- however, the 
spring under the latch will force it up so that it will be ready 
to catch and swing the arm B on the next stroke. If the 
governor mechanism be attached to the rod F, it is obvious 
that, if it acts to depress the latches G, the arm B moves the 
valve-stem D through a less angle, and lets it go so much the 
sooner. The exhaust-valves of the Greene engine are operated 
independently underneath the cylinder, one at each end. 

iio. Corliss Valve-gears. — The Corliss valve is shown in 
principle in Fig. i8i. The usual gear has four valves — two 



212 MECHANICAL ENGINEERING OF POWER PLANTS. 



of them for steam above the axis of the cyHnder, and two for 
exhaust below. In the form shown they are made directly in 
the cylinder-heads. It is perhaps more usual to put them 
upon the sides, as shown in Fig. 182. The characteristic of the 




valve is that the spindle by which the valve is caused to rotate 
is not fastened to the valve, but is independent of it. This 
takes away the objection to the cylindrical cock-valve. The 
valve need not fit tight all about its casing, but must turn 
when its spindle is turned from without. On the type shown 
it will be apparent that ports and passages are of the smallest 



CAM AND RELEASE VALVE-GEAR, 



213 




214 MECHANICAL ENGINEERING OF POWER PLANTS. 

possible length and surface, thus taking advantage of the 
features discussed in par. lOO. 

The second feature of the Corliss valve-gear is the opera- 
tion of the four valves from points on a wrist-plate which is 
made to vibrate back and forth through a considerable angle 
by its connection with the eccentric. The two upper valves, 
Fig. 182, are connected near the vertical diameter of the 
wrist-plate, and the two lower or exhaust-valves connected 
nearer to the horizontal diameter. It will be apparent from 
this peculiarity that the steam-valves will be opened rapidly 
as the engine passes its dead-points, while the exhaust-valve 
will be held wide open during that fraction of the angular 
motion of the wrist-plate during which the link of the ex- 
haust-valve is coming up into line with the centre of the 
wrist-plate and is passing beyond and above that line and is 
returning to its original position. The other steam- and the 
other exhaust-valve are without effect on their openings dur- 
ing the stroke in which their mates are in action. The valves 
usually work in diagonal pairs. 

The third feature of the Corliss gear is the release or trip 
of the steam-valve rods, by which the hold of the wrist-plate 
upon the valve is dropped and the valve closed suddenly by 
weight or spring. The peculiarities of the method followed 
in the detail of this release-gear differentiates many of the 
various Corliss engines from each other. In the very earliest 
forms the detent was thrown off as the valve-rod moved up 
an inclined plane or wedge. Another form throws a cam 
or eccentric into engagement with a curved arm or toe, and 
the pressure of these upon each other forces the rod to let go 
of the catch on the arm of the valve. In all of these forms 
the adjustment of the gear is usually made by the governor, 
so that the speed of the engine varies the length of admission 
by causing the cut-off when the trip occurs. The exhaust- 
valves are positively connected to the wrist-plate so that 
release and compression are constant, while cut-off and expan- 
sion vary according to the work of the engine. 

The fourth feature of the Corliss valve-gear is the closure 
of the valve by a weight or a spring with dash-pots. The 



CAM AND RELEASE VALVE-GEAR. 21 5 

dash-pot is a cylinder in which fits a piston nearly or entirely 
air-tight. As the valve is lifted it lifts the piston in the dash- 
pot. Air enters below in the weighted dash-pot, and when 
the valve is released the weight of the piston, with or without 
the help of additional weights, closes the valve, when the 
retarded escape of air in the dash-pot arrests the motion 
without excessive shock. In the vacuum dash-pot the piston 
fits tightly, and the life of the piston, creating a partial vacuum 
below itself in the dash-pot, causes atmospheric pressure to 
become the weight or spring which closes the valve. The 
compression of the air remaining below the piston performs 
the cushioning necessary to prevent shock. 

111. Advantages of Trip Vaive-gear. — The advantages 
of the Corliss and other trip valve-gear are: 

1. Quick opening of inlet-valves establishes full boiler- 
pressure in the cylinder early in the stroke. It is a feature 
of most of these gears that their construction and operation 
give large port-areas and little friction through the valves. 

2. The inlet-valve closes quickly. The effect of this is 
to increase the area of the work-diagram by giving a sharp 
corner at the point of cut-off instead of a rounded curve. 
A rounded corner at this point has the effect of gradually 
lowering the pressure from wire-drawing as a consequence of 
gradual closure. 

3. This type of gear, being specially adapted for engines 
which are designed to be regulated by varying admission, 
gives the advantage of making the terminal pressure low. 
Such engines secure this regulation, furthermore, without 
introducing irregularities in the exhaust functions by virtue 
of their being always multiple-valve engines. 

4. The ease of adjustment of such independent valves if 
variation at the two ends of the cylinder should be desirable. 

5. The small motion and the period of rest for the steam- 
valves after closure diminish the friction of the valve-gear 
and the attendant loss of power. 

112. Disadvantages of Trip Valve-gear. — The trip valve- 
gear, being almost always a multiple valve-gear, is open to the 
following objections: 



-2 1 6 MECHANICAL ENGINEERING OF POWER PLANTS, 

1. The complication and number of parts in most of the 
gears. 

2. The expense of most of the engines fitted with compli- 
cated gear. 

3. The limitation in rotative speed or number of revolu- 
tions imposed by the necessity of engaging the catches and 
valves. The inertia of the masses precludes an instantaneous 
action in response to the spring or weight, and the snap-and- 
catch action becomes noisy when the springs or similar devices 
have stiffness sufficient to make them positive at speeds faster 
than 150 revolutions per minute. 

4. The trip and the cam valve-gear have this objection in 
common, that the release of the catch and closure of the valve 
must be effected by the governor during that stroke of the 
valve-rod which nominally opens the valve. In other words, 
in a lifting-valve the release must take place before the valve 
reaches its point of greatest opening. This limits the range 
of the ordinary gears of this class w^ith respect to their ability 
to adjust the point of cut-off. To avoid this last difficulty is 
the object of certain designs of Corliss gear making use of 
two parallel wrist-plates (Fig. 183). They can be operated 
with different eccentrics, and thus a wider range of adjusta- 
bility secured. This is particularly well aimed at in the high- 
speed form there presented, in which the trip gear is dispensed 
with, and the cut-off caused to vary by varying the throw of 
the steam wrist-plate motion. Such an engine can obviously 
be run at higher speed than a detachable gear. In the form 
of valve-motion represented in Fig. 184, which presents the 
Bates mechanism, the release of the valves is effected without 
letting go of the valve-arms. The valve-rod is so jointed 
that the strain on the valve keeps the valve-rod folded over 
its centre of motion until the wrist-plate in its motion causes 
the line of strain on the valve-rod to pass outside of the centre- 
line through the wrist-plate pin. When this happens, caused 
by the governor action, the valve-rod unfolds and the weight 
causes the valve to drop shut. 

113. Steam-thrown Valves. — It has been worked out by 



CAM A ATI? RELEASE VALVE-GEAR. 



217 




2l8 MECHANICAL ENGINEERING OF POWER PLANTS, 

several designers to operate the valve of the engine by a 
steam-cylinder instead of by a positive connection by rods to 
the shaft. This peculiarity is the feature of most direct-act- 
ing pumps having no fly-wheel. In the absence of the fly- 
wheel and with constant resistance a pump of this class whose 
piston-rod is connected to its own valve-rod will stop at 
the end of its stroke, with its valve covering the ports 
so that no succeeding stroke can occur. The solution of 
this problem which is most usual is to have the piston of the 
main engine operate a small steam-valve before the end of its 




Fig. 184. 

stroke. This small steam-valve admits pressure to an auxil- 
iary piston in the valve-chest of the main engine, and this 
piston, yielding to the pressure, moves in its cylinder, carrying 
with it the valve of the main engine into the position to admit 
steam to the main cylinder for the reverse stroke. It will be 
apparent that this principle precludes stalling or stopping on 
the centres, because the main valve admits steam to the main 
engine until the valve of the main engine is reversed by the 
auxiliary engine. Such engines can run at any speed or slow- 
ness, and will start from rest when steam is turned on. They 



CAM AND RELEASE VALVE-GEAR. 



219 



must be full-stroke engines working without expansion, and 
have nothing but exhaust compression to keep all strokes of 
uniform length. (See Cornish Cataract, par. 41.) 

The valve-gear of a duplex pump is identical, the only 
difference being that the auxiliary cylinder of the single pump 
has been made to do pumping work instead of merely throw- 
ing the valve of its consort engine. The two cylinders lie 
side by side, and the valve of the first cylinder when it reaches 
the end of its stroke is operated by the working stroke of the 
second cylinder at about the middle of its travel. This, 
peculiarity brings about a pause at the end of each traverse 




Fig. 185. 
of the water-piston or plunger, whereby the water-valves 
have a chance to seat themselves before the current of water 
through them is reversed. 

Almost the only form of mill- or factory-engine using the 
steam-thrown valve was that brought out by the firm of 
Babcock, Wilcox & Co., about the close of the Civil War, 
and presented in Fig, 185. A little steam-cylinder, whose 
piston is H, threw the cut-off blocks G by steam admitted 
alternately on one and the other side of the piston H. The 
period of such admission was controlled by the governor, while 
the main or distributing valve was driven by an eccentric and 
rod in the usual manner. This illustration will serve also as 
an example of short passages for steam and long passages for 
exhaust (par. 100). 



CHAPTER XI. 
REVERSING VALVE-GEARS. LINK-MOTIONS. 

114. Reversing-gears with One Eccentric. — It will be 
apparent from discussions in parts of Chapters VII and VIII, 
which have treated of the setting of valves, that if the valve 
had neither lap nor lead, so that the angular advance of the 
valve-crank was 90° ahead of the engine-crank in order to go 
forward, it could aot be at the same time 90° ahead of a 
crank which was to turn backward. A very simple reversing- 
gear for a valve of this type can be made by having the 
valve-stem driven from a rocker-arm and so constructed that 
the rod of the eccentric can be geared to it either on the 
same side of its centre of motion as the valve-stem, or at will 
upon the opposite side. From the discussion in par. 83 it 
will be apparent that when the motion of the eccentric-rod is 
reversed by the rock-shaft the engine will turn in one direc- 
tion, and when it is not so reversed it will turn in the other. 
When the valve has lap or lead or both, and is intended to 
work expansively, the valve-crank is 90° -{- an angle a, which 
represents the angle AOE in Fig. 142, ahead of the main 
crank. Hence the position of the centre-lines of eccentrics 
for forward and backward motion will be distant from each 
other an angle represented by 180° — 2a, and a reversing 
motion by the method just described is impossible. 

There are two methods of reversmg an engine using one 
eccentric. The first is to have the eccentric loose upon the 
shaft and free to move independently of that shaft between 
two stops which are bolted, keyed, or otherwise secured to 
the shaft. The loose eccentric has a corresponding lug or 



REVERSING VALVE-GEARS. LINK-MOTIONS. 221 

projection which engages with these stops. The angular dis- 
tance between the stops upon the shaft is so adjusted that 
when the first one engages with the lug upon the eccentric- 
disk, the relation of the eccentric-crank to the main crank is 
that which adjusts the valve-gear to distribute steam for for- 
ward motion. The resistance of the valve as the engine turns 
in one direction keeps the lug and first stop continuously in 
contact. If the engine-shaft be turned in the opposite direc- 
tion by operating its valves by hand, the first stop will leave 
contact with the lug, and the eccentric will stand still by reason 
of the friction of its attachments until the second stop on the 
shaft comes in contact with the lug on the eccentric. The 
adjustment of the second stop is such that when it touches 
the lug the relation between the eccentric and the main crank 
is that for distributing steam for backward motion. This 
arrangement of loose eccentric with lug and stops on the shaft 
has been a very favorite design for ferry-boat engines. The 
working of such boats in and out of slips is done by hand- 
working of the valves in any case, and their comparatively 
slow rotative speed and the large masses in the disks and rods 
lend themselves to this arrangement. 

The second single reversing-gear adjusts the eccentric 
through the angle i8o° — 2a by having the latter borne upon 
a sleeve to which it is feathered, so that it must rotate with 
it and the shaft, while the sleeve can be slid lengthwise on the 
shaft under the eccentric. This sliding of the sleeve is done 
by a lever which has a latch attachment so that it can be 
locked in the desired position. The sleeve has a spiral slot 
cut in it, the slot subtending the angle of i8o° — 2a and fit- 
ting a radial pin projecting from the shaft. It will be obvious 
that when the sleeve is slid lengthwise along the shaft the 
slot and pin will twist the sleeve through the angle i8o° — 2a, 
and carry the eccentric through that same angle. The latch 
prevents readjustment except at the will of the runner. This 
makes a very compact reversing-gear, but is limited to engines 
of small size (Fig. 50). 



222 MECHANICAL ENGINEERING OF POWER PLANTS. 

115. Reversing - gears with Two Eccentrics. Gab- 
hooks. — It makes so much simpler a reversing-gear to use 
two eccentrics, one set 90° -J- a ahead of the crank for forward 
motion, and the other set 90° -f- a behind it, which becomes 
that same angle ahead of the crank for backward motion, that 
this type of reversing-gear is much the most usual. There is 
a rod from each eccentric which is to be hooked and geared 
to the valve-stem at will, and the method of bringing the for- 
ward and backward eccentric-rod into gear with the valve- 
stem constitutes the differentiating feature of all forms of 
motions. 

The simplest and oldest device to attach the eccentric-rods 
to the valve-stem is a hook. This hook, called a gab or gab- 
hook, is simply a hole which fits a pin on the valve-stem or 
on a rocker-arm connecting to it, which hole has one side cut 
out and away so that it can be lowered down upon the pin 
or lifted off from it. Of course the two hooks must not be 
engaged with the same pin at once, and many different 
methods are used to take care of the hook and rod which for 
the time being are not to engage with the pin. The simplest 
is a lifting-roller so adjusted that when brought against the 
under side of the rod it lifts it above the plane in which the 
pin travels. This may be done also by lifting a suspending- 
link. Other devices involve the use of cams or bars which 
shut down over the sides of the hook and fill up the hole, 




3^ 



Fig. t86. 

and are held in place by a latch or snap. With these the 
eccentric-rod may slide upon the pin itself, but when these 
appliances are in place the hook is closed and takes no hold 
of the pin. Fig. 186 presents certain forms of gab-hooks. 
The objections to the gab-hook are three: 



REVERSING VALVE-GEARS. LINK-MOTIONS 223 

1. The engine reversed by this means must have a low 
speed of rotation. 

2. The engine has to be of such a character that the 
reversal can be leisurely. It is not convenient to reverse at 
speed with a gab-hook, but the engine must be turning slowly 
when the hook is dropped upon the pin. 

3. The engine must be of such a character that it can be 
started by hand-working of its valves. The reason for this is 
that there is but one position of the main crank in which the 
hook of the forward gear and that of the backward gear coin- 
cide, so that either can be dropped upon the pin and operate 
the valve properly to pass from forward to backward motion. 
This position is the dead-centre, either outward or inward, on 
which the engine-runner would never stop his engine if it 
could be helped, so that hand-starting is compulsory. 

To avoid the objections to the ordinary gab-hook so that 
the engine might be reversed at speed and started in the 
reverse direction Avithout hand-working, the mouth of the 
hook was widened and the sides lengthened so that it took 
somewhat the shape of an inverted letter V. The distance 
apart of the horns of this V hook was made equal to the 
travel of the eccentric-rod plus the diameter of the pin, so 
that, no matter where in its course the pin might happen to 




Fig. 187. 

be, the sides of the hook pressed upon the pin would slide it 
in the direction of motion until it caught into the hook 
proper at the foot of the V. These V hooks were early 
solutions of the problem of reversing the locomotive engine. 
Figs. 187 and 177 give tne general appearance of such hooks. 
116. Link-motion of Howe or Stephenson — The dififi- 
culties attendant upon large-size hook-gears for reversing 
when they came to be applied in high-speed practice brought 
about the development of what have been called the link- 



224 MECHANICAL ENGINEERING OF POWER PLANTS. 



motions. If the forward and the backward hook be made to 
face each other so that one hooks upon the pin from the top 
and the other from the bottom, and if these two hooks be 




I 



joined together on their outer and inner edges by two arcs of 
circles struck from the centre of the shaft, there will be de- 
rived the Stephenson link. The upper hook of the old gear 



REVERSING VALVE-GEARS. LINK-MOTIONS, 



225 



becomes that part of the slot in the Hnk just behind the joint 
of the forward eccentric-rod to the link, and the lower hook 
the similar part of the link-slot behind the joint to the back- 
ward eccentric. The curved profile of the link keeps the two 
eccentrics from undesired motion, and the pin of the valve- 
stem fits in a suitable block in the slot of the link, so that the 
latter is always ready to be moved to bring either forward or 
backward eccentric to drive the valve, while the eccentric not 
required simply vibrates the link around its virtual centre 
without affecting the valve. Fig. 188 shows the typical 
Stephenson link-motion as designed for locomotive practice 
on the Pennsylvania Railroad, and Fig. 189 its skeleton 



Gd 




Ftg. 189. 

diagram. There require to be attached to the link con- 
venient connections to bring the forward or backward eccentric 
into line with the pin and to hold it at the desired position, 
but their construction requires no explanation. 

This simple form of reversing-gear was applied to early 
locomotives turned out in England by Stephenson, but strong 
claims have been advanced by a William Howe for its first 
suggestion in 1843. 

117. Features of the Stephenson Link-motion. — The 
Stephenson link-motion has certain peculiarities. If the 
valve had neither lap nor lead, so that the two eccentrics were 



226 MECHANICAL ENGINEERING OF POWER PLANTS. 

1 80° apart, it would be apparent that the link would vibrate 
around a virtual axis at its middle point, and that when 
the pin connected with the valve-stem coincided with that 
axis the valve would have no motion. The angle between 
the eccentrics is not 180°, on account of lap and lead, and 
hence when both eccentrics are near the horizontal line in 
a horizontal engine they are each moving the link in the 
same direction at top and bottom. That motion, however, 
is usually so small that it does not uncover the laps over the 
port ; or in other words, cut-off takes place before the stroke 
begins. At intermediate points above and below the centre 
the travel of the valve is less than full throw of the eccentric, 
and by reference to Chapters VII and VIII it will be apparent 
that earlier cut-off and greater expansion will be secured by 
this diminished throw, and yet without seriously distorting 
the exhaust events, since the angular advance is not dis- 
turbed. It is no disadvantage in locomotive practice to have 
compression increase with earlier cut-off. The heavy duty 
of the locomotive is in starting its load from rest, and at 
very high speeds on a level track the engine is doing much 
less work, so that it can be operated at earlier cut-off. The 
compression is a decided advantage at the high rotative 
speeds. It is the simplicity of combining the variable cut-off 
gear w^hich is desirable with the reversing-gear which is neces- 
sary, and in one mechanism so simple as to be operated with 
one lever, which has given the Stephenson link-motion its 
popularity for the locomotive. 

The only objection to be urged against the Stephenson 
link is its slight inaccuracy, which produces a variation of the 
lead at different points of cut-off. By reason of the fact that 
the link is raised and lowered, carrying with it the rods, the 
latter are shifted around their eccentric-disks. It will be seen 
that when the angle is varied which the eccentric-rod makes 
with the line through the dead-centre of the engine-crank, 
from which angles are counted, there will be of necessity a 
motion of the valve at dead-centres of the engine-crank, since 
the effect produced is to diminish the angle 90° — a, which 



REVERSING VALVE-GEARS. LINK-MOTIONS. 



227 



is therefore the same as increasing the angular 90° -|~ ^ which 
measures the angular advance ahead of the crank. To 
increase this angular advance ahead of the crank is a thing 
which is done where the lead is to be increased (par. 91). 
The lead, therefore, increases as the cut-off is made earlier. 
The following table shows the extent of these variations in a 
standard locomotive gear, especially when a little worn. 



Notch in 


Travel 

of 
Valve. 


Port-opening, 


Point ofCut-off. 


Point of Release. 




Sector of 
Lever. 


Forward. 


Back- 
ward. 


Forward 


Back- 
ward. 


Forward. 


Back- 
ward. 


Lead. 


20 

19 
18 
16 

14 

12 

9 

8 


5 

4i 

4 

3i 

3i 

2| 
2f 
2* 


1 


1 
1 


2o| 

I9f 
i8|- 
i6i 

14 
12 

f 


I9i 

i8i 

16^ 

14 

iif 

9i 

6| 


23i 

22x1 
22| 

21H 
19-1 

i8| 
17 


23i 
22f 
22| 

20/6 
20A 
I9t'6 


1 

i 



The throw of the eccentrics was 5 inches, the steam-ports i^ inches and the 
€xhaust-ports 2f inches wide. The lap was | of an inch outside and -^^ inside. 

118. Gooch's Link-motion. — To counteract the difficul- 
ties of the Stephenson motion caused by shifting it around 
the eccentric and shaft, Sir Daniel Gooch, a railway motive- 
power engineer of England, reversed the Stephenson link and 




— E3 



Fig. 190. 
made the valve-stem pin slide up and down in the link which 
was suspended, so as to be unable to rise or fall (Fig. 190). 



228 MECHANICAL ENGINEERING OF POWER PLANTS. 

It is obvious that the reversing and cut-off action are retained, 
but the variation in the lead is eliminated. This motion has 
never been popular in America, since for its satisfactory work- 
ing the valve-stem must have considerable length, and the 
design of American locomotives makes it difficult to secure 
this. If the curvature of the link has a short radius, irregu- 
larity in the valve-motion is introduced. 

119. Allan^s Link-motipn. — The Allan link-motion com- 
bines the characteristic features of the Stephenson and Gooch. 
The link and valve-stem are swung from opposite ends of a 
lever pivoted at or near its centre, and variation in position 
of the stem and link is produced by lifting one and lowering 
the other. The advantage of this form is the straight profile 
of the link, which makes it easy to machine in the shops, but, 
like the Gooch link, it has never met much acceptance among 
American locomotive-builders, where the type of outside- 
cylinder engine, which is preferred, makes it necessary to put 
the valve mechanism between the frames under the boiler. 
It has the advantage over the other two that the weight of 
link and of valve-stem partly balance each other so that 
counter-balancing weights or springs are not required as in 
the other forms. 

120. Radial Valve-gear. Joy's Valve-gear. — Variations 
have been made upon the link-motion hitherto discussed in 
the effort to do away with one of the eccentrics or both. The 
eccentrics in fast-running engines are sources of friction by 
reason of their large diameter, and they not infrequently give 
trouble from heating. The general name of radial valve-gear 
has been applied to such valve-motions as transmit a motion 
to the valve-stem from an arm one end of which moves in a 
closed curve and which has another point constrained to move 
in either an open or a closed curve by its connection with the 
frame through levers or slides. The closed curve described 
by the first point is usually a circle, an oval, or an ellipse, 
and motion is imparted from an eccentric or a crank or by 
the connecting-rod. 

The best-known valve-motion of this type is Joy's valve- 



REVERSING VALVE-GEARS. LINK-MOTIONS. 229 




Fig. 191. 




Fig. 192. 



230 MECHANICAL ENGINEERING OF POWER PLANTS. 

gear, shown in Fig. 191 as applied to a marine engine, and 
in Fig. 192 in outline. It has been used quite a little in 
both marine and locomotive service. It will be seen that the 
motion originates from a point on the connecting-rod which 
gives from its connection to a secondary link a reduced 
motion to the lever which drives the valve-stem. The point 
D describes an oval. The other end of the link slides in a 
curved path to provide for the back-and-forth motion of its 
first endo The reversing effect is caused by the angle at 
which the curved slot is inclined. A variation in the point of 
cut-off is produced by the variation in the throw of the valve- 

HORIZONTAL ENGINE WITH JOY'S GEAR. 




Fig. 193. 

stem, which is least when the curved slide is midway between 
its forward and backward position. The slide may be replaced 
by causing the point K to vibrate from its connection to a 
link whose radius is the same as that used in describing the 
slide (y in Fig. 195). The Joy valve-gear is made up en- 
tirely of pin-joints for the moving parts, and gives equal lead, 
cut-off, and port-opening in both gears. The objection to it 
•in locomotive practice is the exposed position of the links 
outside of the frames, where accidental injuries are most likely 
to affect them. Fig. 193 shows this gear applied to a 
stationary engine. 

121. Walschaert Valve-gear. — Almost the only other 
form of valve-gear which has contested with Joy's the sole 
acceptance with locomotive-builders is a Swiss motion which 
bears the above name of its inventor. Fig. 194 shows that 
the double motion is derived partly from the engine cross- 



REVERSING VALVE-GEARS. LINK-MOTIONS. 



231 



head and partly from a crank or eccentric 90° from the main 
engine-crank. The valve gets an aggregate motion from the 
cross-head and from the curved link, and reversing is effected 
by reversing the motion derived from the eccentric-rod when 
the sliding-block is on one side or the other of the fixed centre 




Fig. 194. 

of motion of the curved link. It will be seen that such a 
gear produces no variation in the lead. 

The valve-motion designed for locomotives by Mr. George 
S. Strong has many features similar to the foregoing. The 
motion is obtained from a single eccentric, which has two 
levers attached to the strap. One is rigidly bolted to it, and 
the other connected by a pin-joint. The two levers have a 
common fulcrum-pin which is suspended by a link from a 
block above, whose position can be varied upon a sector. 
The position of the blocks upon the sector determines the 
inclination of the path through which the fulcrum-pin travels. 
The exhaust-valves of the Strong locomotives have their own 
motion independent of the admission. This engine uses 
gridiron valves. 

122. Brown, Marshall, Hackworth, and Angstrom 
Valve-gears. — The valve-gears identified with the above 
names are reversing-motions with one eccentric opposite to 
the crank. The difference between them is mainly in the 
method used to guide the end of the eccentric-rod farthest 
from the shaft. Fig. 195 shows a Marshall gear as applied 
to marine engines. The one end of the eccentric-rod / 
describes a circle concentric with the shaft, and the end 



232 MECHANICAL ENGINEERING OF POWER PLANTS. 



farthest from the shaft swings in an arc controlled by the 

link J and by the position of the 
fixed centre of the link. The 
valve-rod and stem are attached 
to the eccentric-rod /at the point 
which will give the desired throw 
to the valve. If the centre of 
the link J be thrown over to the 
right, the engine will reverse, 
and at intermediate positions the 
throw of the valve is diminished 
and cut-off takes place. The 
Brown gear has a block whose 
inclination is varied, as in the 
Joy gear, and Angstrom uses a 

pair of radius-bars to make a parallel motion and compel the 

head of the rod to travel in a straight path. 




Fig. 195. 




Fig. 196. 

123. Allen Link-motion. — The link-motion first proposed 
by Allen is the one which in a modified form is known as the 



REVERSING VALVE-GEARS. LINK-MOTIONS. 233 

Pius Fink gear. It has no eccentric-rod properly so called, 
but the link is an integral part of the back strap. The 
half of the strap which carries the link has a fulcrum-pin by 
which it is attached to the engine-frame above or below the 
shaft, so that the motion of the centre of the link is an aggre- 
gation of the back-and-forth motion of the strap as a whole, 
and the up-and-down motions caused by the constraint of the 
fulcrum-pin which prevents undesired motion of the point 
where it is attached. Fig. 196 shows the Allen link. If the 
•engine is not intended to reverse, but variation in point of 
cut-off only is desired, the slot in the upper half above the 
fulcrum-pin only is needed. As the valve-stem approaches 
the centre-line of the shaft, its motion diminishes. In the 
Porter- Allen engine the separate exhaust-valve is driven from 
.a fixed point near the end of the slot, giving constant travel, 
release, and compression. The eccentric of the Allen link is 
set opposite or at 180° with respect to the crank. 

124. Link-motion for Riding Cut-off Valves. — It adds 
•considerably to the complication of a valve-gearing which uses 
an independent cut-off valve when it is required to reverse 
the motion of both valves. The cut-off valve may have its 
independent link-motion coupled to the reversing-levers so 
that one motion reverses both the main and the cut-off valve. 
To avoid this complication many designers have arranged the 
■cut-off valve to work with an eccentric 180° distant from the 
main crank, so that the cut-off valve works equally well with 
forward and with backward motion of the main valve. 

Link motions for locomotives operated with cut-off valves 
are identified with the names of Polonceau, Gonzenbach, and 
Meyer. The student is referred to special treatises for study 
of their peculiarities. 

125. Power Reversing-gears. — The Stephenson link- 
motion has been a favorite valve-gear for marine engines, for 
reversing rolling-mill engines and similar massive designs. 
The weights and masses to be moved and the necessity for 
quick action have compelled designers to apply mechanical 
power to reverse the link-motion. Steam power or hydraulic 



234 MECHANICAL ENGINEERING OF POWER PLANTS. 

pressure have been the usual methods. Steam power has been 
appHed first by means of a reversing-engine on whose shaft 
was a screw. The nut of this screw travelling in one direction 
or the other moved the link into forward or backward gear. 
The second plan is to attach the rod of the tumbling- or rock- 
shaft to a steam-piston in a cylinder. This would be a too 
rapid reversing motion, so that it must be controlled for speed 
and the piston must be held still or latched at the desired 
point of the motion of the link. This is attained by attach- 
ing to a prolongation of the piston-rod a second piston whick 
moves in a cylinder filled with water or oil at both ends. The 
motion of this oil-piston from one end of the cylinder to the 
other will be controlled by the passage of the oil through a. 
pipe connecting the two ends of the cylinder through a valve. 
The velocity of motion is controlled by the greater or less 
opefiing of this valve, and when the valve is shut the pistoa 
is locked in place and the link is held. The third form 
applies the principle of steam steering-engines to the link-^ 
motion. The motion of the engine to throw the link is con- 
tinually closing the admission-valve of this auxiliary engine, 
so that continuous motion of the hand is necessary to keep, 
the link moving. When the hand stops the engine stops. 
This prevents the attendant from jumping the valve-gear. 

Hydraulic-pressure reverse-gear is available where water 
under sufficient pressure can be had from pumps or accumu- 
lator. The power cylinder is sufficient with hydraulic pres- 
sure, since a closure of both inlet and outlet valves to the 
piston locks it rigidly in place and holds the link at the 
desired position. The piston-rod of the hydraulic cylinder 
either throws the link directly, or operates a tumbling- or 
rock-shaft to which the link is connected by rods. 



CHAPTER XII. 
VARIABLE CUT-OFF VALVE-GEARS. 

126. Introductory. — The discussions of Chapter VI should 
have made clear the distinction between a throttling-engine 
and a variable cut-off engine. The foregoing treatment of 
valve-gearing should have made it clear that there were several 
ways in which the valve-gearing could be so designed that 
the point of cut-off could be varied at the will of the engine- 
runner by his adjustment of the valve-gear. The conditions 
which make this design to be preferred to an automatic varia- 
tion of the point of cut-ofT by the engine-governor are to be 
met in engines for propulsion, such as the locomotive and the 
marine engine, in engines for pumping and hoisting where the 
work does not vary irregularly, and in many cases of factory 
practice where the variation is in starting the machinery only, 
but not in the regular service of the engine. 

The methods to be used to vary the points of cut-off by 
hand are usually the same as thjose which will be used when 
the governor is to make the point of cut-off vary. It will be 
seen that four general principles underlie the methods which 
will be used in either the variable or the automatic cut-off 
engine to secure this end. 

127. Cut-off Varies by Varying Throw of Valve. — The 
discussion of motion-curves in par, 93 showed that the cut-off 
became earlier as the throw of the valve became less. This 
is the way the link-motions act, and in engines for propulsion 
and for hoisting, which require to be reversing as well, the 
link-motion will always be found. The Allen or Fink link 
(par. 123) can be made an automatic variable cut-off by causing 

235 



236 MECHANICAL ENGJNEEJRIN^OF POWER 

the governor, as the engine speeds up, to lower the valve- 
stem operated by the slot in the link, so as to diminish the 
throw. The slider in that slot can be raised and lowered by 
hand, if desired, by having it mounted upon a screw. 

The second great method of securing cut-off by varying 
throw is to arrange the eccentric so that the effective valve- 
crank can be made less or more. In the discussion of shaft- 
governors hereafter it will be seen that it is quite easy 
to vary the eccentricity of the eccentric without changing its 
angular advance by means of an equilibrium between revolv- 
ing weights and springs. The eccentric can be made to have 
a variable eccentricity by mounting it upon the outside of 
another eccentric which shall be adjustable under the outer 
one. The effective eccentricity of the outer one can thus be 
varied between the sum and the differences of the eccentrici- 
ties of the two eccentrics. 

The third method of varying the throw is to be met in 
cam valve-gears. The profile of the cam can be made to be 
different at different transverse sections. A mechanism which 
slides the cam underneath the roller which it drives will cause 
the valve to open farther and remain open longer when the 
valve-stem is driven by the wider and more prominent profile 
of the cam. This lengthwise sliding of the cam on the cam- 
shaft can be done by hand or by a governor. 

128. Cut-ofT Varies by Varying Lap of Valve. — The dis- 
cussion of lap in Chapter VII, which showed it to be a matter 
of construction of the valve itself, might appear to indicate 
that the lap of a given valve is not a variable. This is true 
for a valve-gear dependent upon one valve only, or in which 
the steam-ports and cut-off edges of the valve are parallel. 
The discussion in par. 96 will have shown that as the lap is 
increased the cut-off becomes earlier. 

Fig. 197 shows the form of riding cut-off valve having the 
simple expedient of making the valve in two parts, which are 
attached to the valve-rod by being fitted to screws on that 
rod. It will be noticed that one screw is right-handed and the 
other is left handed. When the rod is turned around its axis 



VARIABLE CUT-OFF VALVE-GEARS. 



237 



by a hand-wheel or through similar means outside of the valve- 
chest, the two blocks are drawn together or separated accord- 
ing as that motion is right-handed or left-handed. A swivel- 
joint in the valve-rod permits this motion of adjustment, and 



Connects to Condenser 




an indicator bearing a graduated scale can easily be attached 
to the valve-stem connection, so as to indicate the effective 
length of the valve from out to out, and the point of cut-off 
which belongs to each particular length of the valve. 

Fig. 198 presents a scheme for securing a variable lap by 




means of a similar secondary motion of adjustment for the rod 
of the cut-ofT valve. It will be observed that the ports and 
cut-off valve are trapezoidal in plan, so that if the valve be 
sliding back and forth in the position indicated it will have a 
certain lap with respect to the length of the ports. By rotat- 



238 MECHANICAL ENGINEERING OF POWER PLANTS, 

ing the valve-stem, the pinion which it carries will cause the 
valve to slide in a plane farther up in the chest, so that the lap 
at each horizontal line has become longer than it was in the 
position shown. This rotating of the stem and adjustment of 
the plane of the cut-off valve can be effected either by hand or 
by the governor. When it is to be done by the governor the 
mechanism becomes more simple when the method is fol- 
lowed which is shown in Fig. 199, which is the characteristic 




Fig. 199. 

feature of the Rider cut-off valve-gear The flat pl-ane of 
Fig. 198 has become the surface of a cylinder, and the cut- 
off valve is a part of another cylinder. As the spindle of the 
cut-off valve is turned through an angle as it slides up and 
down as usual, the surface of contact with the main-valve 
ports becomes longer and longer, the lap over the ports in- 
creases, and the cut-off grows early. 



VARIABLE CUT-OFF VALVE-GEARS. 239 

A scheme for securing an equivalent for the variation of 
the lap is represented in Fig. 200, in which it will be observed 




Fig. 200. 

that the steam-edge of the port is made with a false seat to 
•which motion can be imparted through the rod C. As cut-off 
takes place with the outer edge of the valve as it approaches 
its central position from its extreme throw, it will be apparent 
that to have the valve-seat moved to meet the valve is to 
produce the same effect as lengthening the lap of the valve 
over a stationary port. It is only necessary that provision 
should be made to vary the angular advance of the eccentric 
which drives the rod C. This shows a balanced valve also 
(par. 104). 

129. Cut-off Varies by Varying Angular Advance of 
Eccentric. — To avail of this method to vary the cut-off, the 
eccentric cannot be positively fastened to the shaft. There 
must be some provision similar to the methods described in 
par. 114 to adjust the relation of the eccentric to the crank, 
or the mechanism of the shaft-governor (see Chapter XIII) 
must be so connected to the eccentric as to produce this 
effect. The objection will be that, while cut-off will become 
earlier with increasing angular advance, the exhaust events.are 
distorted. An exception of note is to be met in the valve- 
gearing of the Buckeye engine, in which the ingenious expedi- 
ent has been adopted of mounting the cut-off valve mechanism 
upon a rocking-arm which is a part of the main-valve gear. 
Increasing degree of expansion without interference with 
other functions follows from simple change of the angular 
advance. 



240 MECHANICAL ENGINEERING OF POWER PLANTS. 

130. Cut-off Varies by Varying Point of Release or 
Trip. — This form of variable cut-off gear has been fully dis- 
cussed in Chapter X. The primary intent of most trip-gears 
is to have the period of the release of the admission-valve 
variable at will. The cam valve-gears can be similarly made 
variable by so arranging the earn itself or the lever which it 
operates that an adjusting mechanism shall cause it to come 
out of contact at the desired point of the stroke. The 
methods for accomplishing this result are very numerous and 
can be quite simple. 



CHAPTER XIII. 
GOVERNORS FOR STEAM-ENGINES. 

131. Introductory. — The governor of a steam-engine is 
the device or appliance whose function is to control the mean 
energy of the steam-engine when the external resistance 
varies. Its functions differ from those of the fly-wheel, which 
has to regulate or supply excess of energy a«d give it out 
when demanded for a short period. As soon as its capacity 
for storing or restoring energy is exhausted a permanent 
change in the speed of the engine occurs, and then the gov- 
ernor must take hold to control and vary the supply of 
energy to the cylinder and thus maintain an equilibrium 
between resistance and supplied energy at the normal or de- 
sired speed. 

The usual condition is that the speed of the engine or 
number of revolutions per minute shall be kept the same, and 
the governor is expected to produce variations in the pressure 
in the cylinder by the methods discussed in Chapter VI. It 
will thus be noted that while the governor is really an appli- 
ance for controlling energy, its immediate function upon its 
way to discharge its principal duty has become to control the 
speed of the engine. It may thus be seen that the governor 
may be expected to do two duties. The first will be to pre- 
vent disaster to the engine in cases where, by some breakage of 
belt or transmission machinery, the load should be entirely 
and suddenly taken off from a large engine. In the absence 
of any governor-device, an engine under this condition would 
*'race," speeding itself up until its own internal friction 
replaced the released load. Usually before this happens 
something else in the way of disaster has occurred from the 
bursting of the fly-wheel by the centrifugal energy developed 

241 



242 MECHANICAL ENGINEERING OF POWER PLANTS. 

within it, or from the entrained water which the steam has 
brought mechanically with it into the cylinder. It is this 
sort of racing due to sudden withdrawal of the resistance 
which has been the strain which has broken the shafts of 
steamers and wrecked their engines. The governor should 
be able so to check the delivery of energy to the cylinder 
that, even under such an accident as this, the racing or running 
away should be impossible. The second function of the 
governor is an extension of the first and increases it. With a 
governor of the first sort it will be expected that the unloaded 
engine will run a little faster than when it is fully loaded. 
The governor which would fulfil the second function would 
be one in which, no matter how the load might vary, the 
distribution of energy per stroke is so exactly proportioned 
to the resistance that the rotative speed of the engine will 
be' constant under all variations. The governor which meets 
this second requirement and under all variations of load 
causes the engine to make the same number of revolutions in 
a given time, and hence each revolution in the same time, is 
called an isochronous governor. A governor to prevent run- 
ning away and racing need not be isochronous. The governor 
which is intended to vary the point of cut-ofT in each stroke 
should be as nearly isochronous as it is convenient to make 
it. It is really the engine which becomes isochronous when 
so governed, and many engines are in use which attain isoch- 
ronism within the limits of ordinary detection. Isochronism 
is more usually approached at high rotative speeds than at 
low (see pars. 35 and 36), but practical isochronism is attained 
with a permitted variation in most cases of two per cent above 
and below the normal. It will be seen that if the governor 
is to depend upon the variation in the engine-speed to read- 
just the supply of energy, that variation of speed must occur 
and must affect the governor before it exerts its control. 
Hence the governor is always "hunting" the engine and a 
little behind it. As the interval is shortened between the 
change of speed and the adjustment caused by that change, 
the engine approaches isochronism more closely. The governor 



GOVERNORS FOR STEAM-ENGINES. 243 

to be isochronous should therefore be sensitive and should 
not be sluggish. 

132. Classifications of Governors. — Steam-engine gov- 
ernors may be variously classed. They may act to throttle 
the steam in the pipe (par. 74), or they may act to vary the 
duration of the admission but not its pressure (par. 75). The 
first class will be called throttling-governors, the second class 
cut-off governors. 

Governors are nearly always founded upon an equilibrium 
or balance of forces at the desired or normal speed, so that the 
disturbance of that equilibrium due to a change of speed calls 
for an adjustment of the mechanism, and the motion of the 
adjustment alters the distribution. A direct relation between 
speed and centrifugal force has long induced designers to plan 
their governors in dependence upon the energy generated in 
revolving weights by centrifugal force. A second classifica- 
tion, therefore, would be to divide governors into centrifugal, 
inertia, and resistance governors according as variation in speed 
is desired to produce a variation in equilibrium betw^een these 
forces and some other in opposition to them. The class of 
centrifugal governors may be divided into two according as 
the acceleration due to centrifugal force is balanced by the 
force of gravity or the tension of springs. The spring-gov- 
ernors are sometimes called balanced governors, because most 
of them will work in any position. The resistance-governor 
is operated by a variation in the resistance offered to motion 
by some part or organ of its construction. This is most 
usually done by the use of a fluid, when the governor becomes 
a fluid governor, or by a braking action which is stronger or 
weaker than the normal according as the speed increases or 
diminishes. The inertia-governors depend upon the principle 
that the variation in inertia of a revolving mass follows in- 
stantly upon a tendency to vary the speed, and change in 
position following the change of inertia adjusts the mechan- 
ism. 

Governors may be classified again according to the method 
adopted to effect change in the valve-gear or the distribution. 



244 MECHANICAL ENGINEERING OF POWER PLANTS. 

Under this grouping they would appear in three classes. The 
first and most generally used might be called position-gov- 
ernors, in which the weights or masses produce their effect to 
diminish or increase the energy admitted to the cylinder as 
the position of these weights is varied by the preponderance 
of weight or some other of the forces which are in equilibrium 
at normal speed. 

The second group would be called disengagement-gov- 
ernors. These are of several types, but their underlying prin- 
ciple is that at normal speeds the governor is without effect 
upon the regulating-train or is disengaged from it. As the 
speed varies above and below that of normal rate the gov- 
ernor engages or puts in motion a train of mechanism whereby 
the supply of energy is diminished or increased. This is a 
specially useful type of governor for water-wheel motors, but 
can easily be applied to engines. It will be seen, however, 
that it is likely to be a better type for safety against racing 
than to secure continuous isochronism. 

The third group in this class will be called differential 
governors. In this class a certain normal speed is fixed by 
braking or a uniform resistance or a separate mechanism, and 
when the governor revolves at this speed it is without effect 
upon the regulating-train. Above that speed or below it the 
difference causes a motion of readjustment to take place, and 
this difference according as it is positive or negative closes or 
opens the supply of energy. 

Governors may be divided again according to the arrange- 
ment or disposition of their mechanism. This gives rise to 
the division into spindle-governors, which revolve around a 
vertical axis or spindle, and shaft-governors, which revolve 
in a vertical plane with the main shaft of the engine as their 
axis or around an independent horizontal axis. The class of 
shaft-governors requires no connecting mechanism between 
the engine-shaft and the governor. The spindle-governors 
are connected to the engine-shaft by belting or gearing or 
both. 



GOVERNORS FOR STEAM-ENGINES. 



245 



133. Fly-ball or Watt Conical Pendulum Governor. — 

James Watt in 1784 made application of the conical pendulum 
principle to the steam-engine as a means of controlling its 
energy. It had been used previously as a means of regulat- 
ing clockwork, but lends itself so easily to the requirements 
of steam-engine practice that it has been the foundation of 
nearly all governing apparatus used until quite recently. 

As applied in the early Watt engines, the governor con- 
sisted of two heavy balls suspended by links from a pin con- 
nection in a vertical spindle. The spindle is caused to 
revolve by belting or gearing from the main shaft, so that as 
the speed increases centrifugal force causes the ball to revolve 
in an orbit farther and farther from the spindle. The posi- 
tion of these balls can be made to vary a train connected with 






Fig. 205. 

controlling valves, so that the admission or the throttling shall 
vary directly with their position. This makes this governor 
a typical position-governor. The connection of the balls with 
the train may be made by links from the balls to an adjusting 
collar on the spindle, or the links from the collar may be 
attached to the suspending links between the balls and their 
joints, or the suspending links may be prolonged beyond their 
point of support, and the regulating-train attached to these 
prolongations. The first plan produces the greatest change 
for a given change in the orbit of the balls. The other plans 
give usually greater leverage upon the regulating-train, so as 
to make lighter balls as effective as heavier ones arranged in 
the other way. Fig. 205 presents typical arrangements of 
the fly-ball or Watt governor. 



246 MECHANICAL ENGINEERING OE POWER PLANTS. 



134. Theory of the Watt Governor. — The theory of the 
conical pendulum-governor depends upon the balance between 
the effort of gravity represented by the line w in the left- 





FiG. 206. 

hand diagram in Fig. 206 and the acceleration caused by cen- 
trifugal force represented by c in that same figure. If h rep- 
resent the vertical height on the spindle between the joint 
of the arm and the plane in which the balls revolve when the 
spindle makes n revolutions per minute, we have, by similar 
triangles, 

h w 



But 

Hence 

If 

then 

or 



r c 

_ Mv' _ 



V 



W V 

g ^ 



h = 



2nrn 
g 



47r^ 



X . Q J 



h .— a constant X 



In other words, the distance of the plane of the balls below 
their point of support varies inversely as the square of the 
number of revolutions per minute. It will therefore be 
apparent that there will be a height h belonging to every 



GOVERNORS FOR STEAM-ENGINES. 247 

speed, so that the balls will be at their highest point at the 
highest permissible speed, and the valve operated by such a 
governor in a throttling-engine should be tightly closed by 
such maximum rise of the balls, 

135. Defects of the Fly-ball Governor.— The fly-ball 
governor as thus constructed is a satisfactory device to pre- 
vent racing, but it is not isochronous unless made so by 
modification or by peculiarities introduced into the regulating- 
train or into the valve which it controls. It will be apparent 
that the opening of the valve or mechanism to admit more 
pressure to the cylinder is done by the weight of the balls. 
In large engines or where heavy masses are to be controlled, 
the balls must have suitable weight or mass to give the gov- 
ernor power to overcome the resistance of the valves and 
train and work quickly. It will be equally apparent, however, 
that the weight or mass of the balls will make them reluctant 
to yield promptly to a change in speed by reason of inertia 
or living force stored in them. Furthermore, increased 
weight in the balls increases friction at the swinging joints, 
and friction is further caused by any cramping action when 
balls are driven by the spindle, and changes of speed cause 
either balls or spindle to twist at such joints. The inertia 
(which is counted on as a means of regulating in the newer 
governors) made the old fly-ball governor both sluggish and 
lacking in sensitiveness. Moreover, the massive balls had to 
turn slowly to prevent the storage of too much energy in 
their revolving mass. Where the spindle principle has been 
retained and gravity is employed to open the valves when the 
speed falls, four types are to be noted in the search for closer 
isochronism. 

136. Loaded Governors. — The loaded governor is an 
early solution of the problem of securing power in a governor 
without adding to the revolving mass of the balls. Fig. 207 
illustrates a loaded governor as worked out for the Porter- 
Allen engine. It will be seen that the weight being placed 
on the spindle and symmetrical with the axis tends to pull 
the balls inward with a constant effort independent of the 



248 MECHANICAL ENGINEERING OF POWER PLANTS. 




GOVERNORS FOR STEAM-ENGINES. 249 

Speed. The effect of this is to increase the force represented 
by the line w as shown in the right-hand diagram of Fig. 206, 
which is to increase the value of Ji which corresponds to any 
value of 11. This can only be done by increasing the constant 
in the second member of the equation for //in par. 134, so that 
the given change in speed produces more change in height. 
Or, in other words, the given change in height will take place 
with a less alteration in velocity. This has therefore increased 
the sensitiveness of the governor, but not its friction. Fur- 
thermore, in the actual governor, as the weight for closing the 
valves is taken a!way from the balls the velocity of the gov- 
ernor-spindle can be greatly increased. Hence the governor 
takes less time to act upon a change of speed in the engine, 
because the governor can turn faster than the engine and it 
takes less time to act upon such change of speed. The loaded 
governor appears in several other forms among the designers 
of European engines, but the principle in all is the same. 

137. Parabolic Governor. — It will be apparent from the 
equation 

// :r= constant X -? 

II 

that the governor which should be perfectly astatic or should 
give perfect isochronism should be one in which h should 
travel through its widest variation for the least change in the 
value of n. The smallest change in speed should make the 
plane of the balls travel to its lowest limit for a decrease, 
and to its highest limit for an increase, in speed. At their 
highest limit they close their valve tight, and at their lowest 
limit they open it wide. Stated otherwise, the mechanism 
of the governor should be such that not only an actual change 
of speed, but merely a hint or suggestion of an intention to 
change, should be required in order to cause the governor to 
readjust the supply of energy in the proper way. This con- 
dition is met in the governor mechanism by causing the balls 
to travel outward from the spindle upon the arc of a parabola. 
A parabola has the property that its subnormal is constant 



250 MECHANICAL ENGINEERING OF POWER PLANTS, 

and equal to the parameter. The arms which connect the 
balls to the spindle can be made normals to a parabola hj 
their construction (Fig. 217), and the height h in the eq-uation 
of par. 134 and of the diagram Fig. 206 will then be this con> 
stant subnormal. In Fig. 217 the curve LC is the evolute of 




a parabola, and a flexible connection unwrapping from this 
curve will compel the ball ^ to move upon a parabolic curve. 
No matter in what part of the arc of the parabola the balls 
may be revolving, as centrifugal force sends them out the 
height h remains the same; whence it follows that the balls 
are in absolutely unstable equilibrium, and will when wide 
open or closed tight adjust the regulating-train with no change 
whatever in the value of 7i, This makes such a governor 
hypersensitive, or too sensitive to be of practical use. The 
effect of sudden changes of load with such a governor would 
be to introduce momentary departures from the normal or 
mean speed. This difficulty of the exact parabolic governor 
is corrected in two ways. First, by attaching a dash-pot to 
the governor-spindle, and secondly, by the use of approximate 
parabolas for the path of the balls. The dash-pot method 
attaches to the adjusting spindle a piston which fits in a small 
cylinder filled with oil. The resistance offered by the oil to 
displacement from one end of the little cylinder to the other 



GOVERNORS FOR STEAM-ENGINES. 



251 




Fig. 208. 



through and around the piston serves as a brake, to prevent 
jumping or racing or hunting, while no real resistance is 
offered to changes of position. The 
approximate parabolic governor is 
sometimes called the cross-armed 
governor. The suspending links are 
hung from points which are the 
centres of a circle whose radius is 
the radius of curvature of the parab- 
ola for that part of its arc over 
which the ball is to travel {BC in Fig. 
217). This type, first introduced by 
Farcot in France, has been widely 
used. Greater power can be given 
to such a governor by loading it. 
Fig. 208 shows the Steinlen loaded 
approximate parabolic governor. 

138. Balanced Governor with- 
out Spring. — Many forms of gover- 
nor have been devised to secure an approach to isochronism 
by aiming at balancing the effect of gravity in part and thus 
make the governor more acutely sensitive to changes of 
speed. The direction in which this has been sought most 
frequently is to connect a second smaller weight to the sus- 
pending link on the opposite side of the vertical spindle. 
This arrangement has taken many forms, but perhaps that 
shown in Fig. 209, which shows the Buss governor, presents 
a European type as well known to Americans as any other 
of its class. The Babcock & Wilcox governor, shown in 
Fig. 210, will stand as representative of another solution, 
in which the weight of the balls is eliminated from the 
forces in action by the connection through the radius-rods 
P to the revolving spindle. Since the lengths of the rods n 
and P can be so related to each other that P shall be one half 
the length of n. a parallel motion will be formed so that the 
balls fly in and out, not in arcs of circles as in previous spindle 
designs, but in a horizontal plane. They do not have to be 



252 MECHANICAL ENGINEERING OF POWER PLANTS. 



lifted, therefore, in order to travel in a larger circle, and an 
increased speed is not needed to maintain them in their 
advanced position. That there may be a force to bring them 
in, the spindle is lifted by the weight /^operating through a 
bent lever. The proportions of this lever and the variation of 





Fig. 209. 



Fig. 210. 



its arms are so adjusted that the centrifugal force at any given 
speed will just balance the weight in all its positions. Any 
increase in speed will cause the balls to preponderate, and a 
diminution of speed will cause the weight to preponderate. 
By connecting the spindle to the cut-off mechanism, the 
cut-off will be changed until the speed comes again to the 



GOVE/^NOKS FOR STEAM-ENGINES. 



253 



standard where the force resident in the weight balances the 
downward pressure on the spindle due to the centrifugal 
force of the balls. By increasing the weight [^ or diminishing 
it the desired speed can be varied. The dash-pot serves to 
prevent instability or jumping. 

139 Balanced or Spring Governors. — A much nearer 
approacli to isochronism is made by those forms of governor 
which substitute a spring for the force of gravity to draw in 
the balls and open the valve when the speed falls. This has 
been a very fruitful field for governor designs, and successful 
spindle-governors and all shaft-governors depend on this prin- 
ciple. They approach isochronism more closely because the 
tension of the spring can be made to increase as the centrifu- 
gal acceleration increases, so that the revolving weight and 
the spring are in equilibrium only at the normal speed. 

Early forms of successful spring-governors of the spindle 
type are Pickering's, Fig. 211, and Waters', Fig. 212, Gard- 




FiG. 211. 



Fig. 212. 



ner's and Wright's, Fig. 213. In Pickering's governors the 
jointed link of the typical fly-ball spindle-governor is replaced 



254 MECHANICAL ENGINEERING OF POWER PLANTS. 



by a flat steel blade to which the balls are secured rigidly 
through their centre of gravity. There are usually three 
balls, and the curve of the springs is such that in action they 
take the curve known as the cyma-reversa. In the Waters 
governor the balls are similarly mounted on flat-blade springs 
which are bent before fixing to the spindle into the form 
shown. The object in both cases is to get a balance between 
centrifugal force and the resilience of the spring at the normal 
speed only, and a preponderance of one effect over the other 
at all other speeds. In these designs the balls are small and 
light and revolve at high speed. 





Fig. 213. 

The first spring governor using an initial tension of the 
springs was patented by Chas. T. Porter in 186 1. His claim 
was for the idea of giving to the spring of a centrifugal gov- 
ernor an initial deflection of such amount that in every position 
of the balls the radius of the circle described by them and 
the distance through which the spring is deflected shall bear 
a nearly constant ratio to each other. 

140. Shaft-governors. — When the vertical-spindle idea is 
abandoned and the revolving mass is attached to the horizon- 
tal shaft of the engine so that it turns in a vertical plane, the 
balanced and spring principle is a necessity, and gravity must 
be eliminated. The methods pursued in the design of shaft- 
governors differ very widely, while yet possessing much in 
common. Two pivoted masses or weights are disposed 
svmmetricallv on the two sides of the shaft, and their ten- 



GOVERNORS FOR STEAM-ENGINES. 255 




256 MECHANICAL ENGINEERING OF POWER PLANTS. 



dency to fly outwards is resisted by springs either in simple 
spiral form or in flat-leaf form. The outward motion of the 
weights closes the admission-valve earlier, and the inward 
preponderance of the springs closes it later. Equilibrium 
exists only at a certain fixed speed, and that speed can be 
varied by varying the spring tension. Fig. 2 14 shows a shaft- 
governor of this type in its position of early cut-off on the right 
and latest cut-off on the left. 

141. Inertia-governors — Fig. 215 will serve as a type of 
the governors which are planned to produce their controlling 




Fig. 215^. 
effect by the change of position which will occur when a 
weighted lever B, pivoted at P, finds that the fly-wheel which 
carries it is lagging behind or overrunning the normal speed. 
At the normal speed a weighted lever occupies a certain posi- 



GOVERNORS FOR STEAM-ENGINES. 



257 



"tion between the stops shown in the cut in equilibrium with 
the spring tension, which at rest would hold it against one of 
them. When the load varies the speed of the fly-wheel, the 
revolving weights keep on at their previous speed, thus chang- 
ing the relation between the lever and the fly-wheel, and 
adjusting the admission mechanism until the normal speed is 




Fig. 2I5«. 
regained. This can also be done by mounting the weighted 
arm nearer the circumference of the fly-wheel, or balancing the 
drag or lag of the weight due to inertia by a proper spring. 
Fig. 216 shows a construction of this sort. 

The instability of inertia-governors, which is the conse- 
quence of their sensitiveness, makes it necessary that many 
of the forms should be steadied fr®m too rapid fluctuation 
by dash-pots. 



258 MECHANICAL ENGINEERING OE POWER PLANTS. 

142. Spindle- and Shaft-governors Compared. — The 
shaft-governor must be a cut-off governor. The spindle-gov- 
ernor may be either a throttHng or a cut-off governor. The 
shaft-governor turns at the speed of the engine, and is valu- 
able only at high rotative speeds. The spindle-governor can 
turn faster than the engine if desired, and can work at low 
rotative speeds. In some recent designs the shaft-governor 
has been geared from the main shaft so as to be run at a 
different speed. The shaft-governor is compact, and is 
directly connected to the engine-shaft, and therefore prompt 
in action. The spindle-governor is connected either by belt 
or shaft to the main shaft, and a breakage of such belt or the 
accident of its slipping or running off its pulley permits the 
engine uncontrolled to run away. The balls drop as the 
governor ceases to turn, and the valves open wide, letting full 
power on the engine. 

143. Resistance-governors. — The class of resistance-gov- 
ernors is less in use under high-speed conditions than it was 
when rotative speeds were low. A very successful form of such 
governor was one in which the opening of the throttle-valve 
was controlled by a rod attached to a weighted piston in a 
little cylinder. A small pump operated by the engine-shaft 
forced oil or water under this piston, while a graduated orifice 
permitted it to flow back into the suction of the pump. 
When the engine speeded up, the oil or the water was pumped 
into the cylinder faster than it could flow out, so that the pis- 
ton was lifted and the energy reduced. When the pump and 
engine worked too slowly the weighted piston descended and 
more energy was admitted to the cylinder. 

Another form of resistance-governors has a propeller-wheel 
revolving in oil within the cylindrical casing. The revolution 
of the inclined blades tends to force the propelled shaft 
lengthwise, and this tendency is resisted by weight or spring. 
When the engine speeds up above the normal, the spring is 
compressed and the weight lifted ; and conversely, as the speed 
falls the weight or spring slides the shaft. Another form 
replaces the propeller by a paddle-wheel which turns in oil 



GOVERNORS FOR STEAM-ENGINES. 



259 



within a ribbed casing. The paddle-wheel tends to carry the 
oil around with it, and the oil catching on the ribs tends to 





revolve the casing. This tendency is resisted by a weight 
acting upon an increasing leverage, so that equilibrium can only 



260 MECHANICAL ENGINEERING OF POWER PLANTS. 

exist at a definite speed. In these two latter forms the posi- 
tion of the spindle and of the casing as determined by the speed 
adjusts the admission of energy to the cylinder. (Fig. 218.) 




Fig. 2i8„ 



Resistance-governors are isochronous in principle, but lack 
sensitiveness to respond instantly to minor variations of 
speed. The objection to them is that they absorb continu- 
ously a certain amount of power, while in the balanced types, 
when no rearrangement of forces occurs, nothing but friction 
has to be overcome. Resistance-governors will become large 
in proportion as the density of the fluid decreases. This has 
stood in the way of attempts to make fan-governors which 
would revolve in the air. The superior viscosity of oil makes 
it a better resistance than water. 

144. Electromagnetic Governors. — Governing devices of 
this sort have been applied with success in central-station 
work, both with steam and water as a source of motor energy, 
where the resistance is the generation of electric current by 
dynamos. In this case the speed and power of the engine 
are controlled directly by the resistance by simple devices. 
A governor of such sort consists of an electromagnet or 
solenoid to which current is supplied from the line wire. 
When the electromotive force rises beyond the normal, a 
motion of the armature towards the magnet takes place against 
the force of the weight or spring. The latter is so adjusted 
as to hold the armature in a fixed position at a normal speed 
and intensity of current. It is only necessary to connect the 



GOVERNORS FOR STEAM-ENGINES. 26 1 

armature to the valve-gearing by convenient means. When 
the spring is in excess there is too Httle current, and more 
energy should be admitted. When the magnet is in excess 
there is too much current, and the energy of the engine should 
be cut down. Governors of this sort will vibrate on each side 
of the mean intensity of the current and keep up a perpetual 
approach to isochronism. 

145. Dynamometric Governors. — Designers of governor 
appliances for their engines have sought to make the resist- 
ance control the effort in the cylinder directly, and without 
having to make use of variation of speed indirectly to control 
the effort. While the electromagnetic governors just dis- 
cussed (par. 144) belong to this class in one sense, they are 
indirect methods except where the work of the engine is the 
generation of electric energy. The best known attempt to 
solve this problem directly was to make the belt-wheel a sort 
of transmission-dynamometer. The belt-wheel was not 
keyed to the shaft, but was driven by the latter through a 
second wheel whose arms were connected to the arms of the 
belt-wheel by means of springs. It is obvious that with a 
given resistance in pounds on the belt-wheel the two sets of 
arms would separate until the stress in the springs balanced 
the resistance. From that time on the two wheels would 
remain in the same relative position until there was a change 
in the resistance, to which the springs would instantly respond 
and produce a new relation of position. The change in the 
angle between the driving arm on the shaft and the driven 
arm of the belt-wheel was made to vary the admission, so that 
the energy of the cylinder varied directly as the load. Such 
a governor was properly called a " weigh the load " governor. 
The difficulty connected with it and with the other governors 
by which the same object has been sought has been that the 
adjustment of the valves could not be controlled within suffi- 
ciently narrow limits. Even with dash-pots to deaden the oscil- 
lation it has not been convenient to secure isochronism of the 
engine. It was hypersensitive, and adjusted the valve-gear 
throu.gh a wider range than actual variation in the load required. 



262 MECHANICAL ENGINEERING OF POWER PLANTS 



146. Safety-stops. — It will have been noticed from the 
preceding that in the case of fly-ball governors the fall or drop 
of balls in gravity types and the drawing in of the balls in 
spring types are the motions by which the valves are opened 
wide. This fall or drop of balls will happen in belted gov- 
ernors when the belt runs off and breaks. As soon as the 
engine is released from the control of the governor, and the 
latter from its position admits the maximum energy to the 
cylinder, the engine runs away, with probable disaster in its 
train. To diminish this danger many forms of governors 
have attachments which are called safety-stops. Their object 
is to close the valve controlled by the governor when the latter 
shall have lost its normal action by some breakage so that the 
balls fall. They are of two kinds, mechanical and electrical, 
In the mechanical safety-stops the usual underlying principle 
is to have a detent or trip which the governor in its normal 
position does not touch,, but which will be released should the 
drop of the balls permit the descent of a rod or lever to its 
lowest point. Such drop of the balls will release the detent, 
which shall permit the action of a spring or weight powerful 
enough to close the valve when thus released. In many con- 
structions the setting of the weight or spring and its catching 
by the detent will be done by hand after the engine has 
reached its normal speed and the rotation of the balls has 
lifted the tripping-rod out of the way. In another form the 
spring is set by a ratchet motion, so that it sets itself after the 
normal speed is reached. 

The electrical safety-stops usually act in essentially the 
same way, but the convenience for the transmission of power 
which is offered by electric methods permits their functions 
to be extended. A very practical form of electrical safety- 
stop has a weight or spring powerful enough when released 
to force the balls to the top of their range, and close off 
admission to the cylinder. This weight or spring is held out of 
action by a detent attached to the armature of an electromag- 
net. The armature may be held away from the magnet with 
a spring of graduated force, so that the normal current in the 
coil shall not be able to draw the armature to the magnet and 



GOVERNORS FOR STEAM-ENGINES. 263 

thus release the weight. Overspeed, exciting the magnet 
beyond the equilibrium-point, will release the detent, releasing 
the weight and throwing the governor-balls up. This same 
result can be attained by differential currents. A convenient 
and useful extension of this idea has been to connect the 
releasing detent by buttons or switches to different rooms 
or departments. In case of accident in such department, by 
pressing the button or throwing the switch the weight con- 
trolling the governor-ball would be at once released and the 
driving-engine would be stopped. 

Automatism with instantaneous action is a prime requisite 
of such devices, and it is very desirable that they should not 
have to depend upon the setting or memory of the engine- 
runner to be made ready. 

147. Marine-engine Governors. — The locomotive and the 
traction engine commonly use no governor. Their resistance 
does not vary suddenly, and a human intelligence must always 
be at hand to' control them in any case. In marine engines, 
however, while in smooth waters the same condition prevails, 
in rough weather the pitching of the vessel may release the 
screw from its resisting medium and suddenly take the load 
off the engine. Obviously this is a source of danger both to 
the long and flexible shaft and to the screw itself when it 
suddenly re-enters the water while moving at too great 
velocity. Many marine engineers prefer to meet thjs diffi- 
culty by keeping one of their staff continually at the throttle- 
valve in bad weather, and no form of revolving governor 
exactly meets the case. Some of the shaft-governors operat- 
ing by springs independently of gravity would meet the case 
most nearly, but for the size of the engines in question and 
the increased complications and weight which would be intro- 
duced. A form of marine governor which has been intro- 
duced in many marine engines is a species of pendulum 
arrangement operating a valve in the steam-pipe. Fig. 219 
shows a general detail of such a device. When the vessel is 
on an even keel, the pendulum attached to a spherical casing 
hangs vertically, and all steam-openings coincide so as to 
leave free passage from boiler to engine. As the ship pitches' 



264 MECHANICAL ENGINEERING OF POWER PLANTS. 

it changes the angle of the steam-pipe, to which a fixed casing is 
attached, while the pendulum-ball remains vertical. The effect 
of this pitch or send of the ship slides the openings past each 
other, and throttles the passage for steam to the engine. If the 
pitch is enough to send the openings past each other, no steam 




Fig. 219. 
can get through. The pendulum swings steam-tight by means 
of flexible or spherical joints at the opening through which it 
protrudes. Most engineers even with such a governor attached 
to their engines do not relax their vigilance at the throttle. 

148. Connections of the Governor to Control the 
Engine. — The student is referred to the discussion in Chapters 
VI and XII for the methods which may be used to make the 
governor in any of its forms control the speed and energy of the 
engine. The number of combinations possible is very great, 
since almost any kind of governor can be applied to produce 
variation in the point of cut-off by the methods discussed in 
Chapter XII. The methods for hand-adjustment of such varia- 
tion are usually made automatic by properly gearing the gov- 
ernor mechanism to the mechanism which operates the valves. 



CHAPTER XIV. 
ENGINE FOUNDATIONS AND BED-PLATES. 

149. Introductory. — In the chapters which have preceded, 
the general features of the steam-engine have been examined 
in their relation to the steam-engine as an appliance for bring- 
ing the expansive force of steam to produce a regulated 
motion. This discussion of the subject rests directly upon 
the underlying general principles of science, and is independent 
of much which belongs to detailed construction. This dis- 
cussion belongs, therefore, to the professional side of steam- 
engine construction, rather than to steam construction as an 
art. In the chapters which follow the practical details of the 
construction of a number of types has to be included. It will 
be sought to cover as wide a field of practice as space will 
permit, wjth the view to familiarizing the reader with success- 
ful and standard details of engine-building. The underlying 
principles of the treatment will be to imagine an engine 
delivered to the power plant disconnected and in parts, and 
a clinical discussion is to be held upon each part as the engine 
is assembled in its place and made ready to be run. 

150. The Bed-plate of a Horizontal Engine. — It will be 
recalled that the typical power-plant engine consists of a bed- 
plate (par. 11) to which, as the fixed link of a chain of mech- 
anism, all other parts of the engine are attached. To this 
bed-plate the cylinder will be attached at one end and the 
revolving shaft at the other, while the guiding and transform- 
ing mechanism must be steadied and aligned by it. This 
bed-plate will therefore be a mass of metal of sufficient weight 
and strength to take care of the forces at play in the mechan- 

265 



266 MECHANICAL ENGINEERING OF POWER PLANTS. 

ism without springing or distortion. Since weight is no 
objection in stationary engines, but is rather an advantage, it 
will be folind that cast iron is much the most usual material 
for bed-plates in such engines. In the locomotive, on the 
other hand, wrought-iron forgings form the bed-plate or frame, 
and for marine engines steel castings or a combination of 
castings and forgings have been much used recently. 

The bed-plate of a vertical-cylinder beam-engine, such as 
is usual in river-boat practice, is often called the sole-plate. 

The ordinary bed-plate of a horizontal engine appears in 
a comparatively small number of typical designs. Historically 
an early type is known as a tank or box bed-plate. It con- 
sists essentially of a box very much longer than it is wide, 
without top and often without bottom. The sides are made 
up of a combination of -mouldings, and the top of the sides is 
formed into wide flanges upon whose upper surface are bolted 
the cylinder and guides and the crank-bearing of the shaft. 
The space between the sides gives room for the motion of 
crank and connecting-rod. It doubtless received its name 
from the practice with condensing engines of utilizing the 
area below the cylinder and mechanism to accommodate the 
tanks used for the hot or the cold well (par. 50). Fig. 225 
shows a tank bed-plate of the ordinary type. It may also 
derive its name from its resemblance to a cast-iron trough. 

An improvement upon the tank bed-plate seeks to dis- 
pose of the metal required in a bed-plate more economically in 
the line of the stresses. It appears in many forms identified 
with the names of a number of various builders. That which 
is usually identified with the name of Corliss in America 
transforms the bed-plate into a brace between the two inde- 
pendent castings of the crank-bearing and cylinder. Each of 
these has its own supporting foot or pedestal, and the bed is 
a casting bolted to each, and either not supported by any 
contact with the foundation or by a central foot only. This 
form of bed-plate is sometimes called the girder bed-plate 
because the shape of the brace, in order to resist the strains 
upon it, becomes that of an I in both the vertical and in the 



I 



ENGINE FOUNDATIONS AND BED-PLATES. 



267 




1 



1 



268 MECHANICAL ENGINEERING OF POWER PLANTS. 




ENGINE FOUNDATIONS AND BED-PLATES. 



269 



horizontal plane. Fig. 226 represents a standard bed-plate 
of this type, and Fig. 227 shows a section through the girder 
(see Fig. 182 also). 

A modification of the Corliss bed-plate is identified with 
the name of Tangye of England, in which the cylinder over- 
hangs the end of the bed-plate proper without a supporting 
pedestal or foot. This gives to the bed-plate its greatest 




Fig. 227. 



mass around the guides, and the crank end is moulded with 
easy curves to clear the space required for the motion of the 
crank and connecting-rod. Fig. 228 may stand for this design 
as well as Figs. 92, 95, and others. The advantage of the 
Tangye (sometimes also called the Porter) bed-plate is the 
convenience of having the bottom of the cylinder exposed 
beyond the foundation, to take the exhaust-pipe or drip to 
a point into which water will naturally gravitate. Further- 
more, the cylinder is free to expand with heat all in one 
direction, without producing a tendency to flex or distort the 
bed-plate. 

The Tangye and Corliss bed-plate designs are susceptible 
of combination or modification almost indefinitely. Fig. i 
shows such combination, and it will be found a feature of other 
types illustrated. The ** straight line" engine (Fig. 229) 



270 MECHANICAL ENGINEERING OE POWER PLANTS, 




ENGINE FOUNDATIONS AND BED-FLATES 2J\ 

■carries the principle of permitted expansion to its logical end 
by having the crank-bearings tied to the cylinder by straight- 
hne braces bolted to both, but the cylinder is not fastened 
to the foot which supports it, but simply rests upon a bearing- 
surface. The engine can be designed to have all components 
downwards upon the pedestal in the absence of rigid connec- 
tions, which removes the tendency to distort in expanding. 

151. The Bed or Frame of a Vertical Engine. — It has 
been seen (pars. 17 to [9) that the vertical engine has the 
cylinder almost always over the shaft. Hence the frame 
becomes a proper casting to carry the crank-shaft from which 
a suitable columnar structure shall arise to carry the weight 
of the cylinder and serve also to guide the cross-head. The 
general appearance of these columnar castings In the usual 
marine engine has given them the name of A frame (Fig. 18). 
In recent designs, to secure greater accessibility for the 
mechanism one side of such frames is made of hollow steel 
columns or rods, such as are fitted on the engine shown in 
Figs. 15, 17 and 53. Accessibility is a prime necessity of 
good design for vertical engines of this class, and is much 
better secured with such open frames. 

In beam-engines the bearing for the beam requires to be 
so designed as to keep satisfactory alignment. In early 
designs it will be found to resemble a massive column or pillar 
(Figs. 60 and 91); In later engines a nearer approach has 
been made to the A frame or gallows-frame usual in river- 
boat practice. The gallows-frame in recent large engines is 
made of steel plate moulded into box-girder shape and 
stronq-lv braced. 

The weight and strength of bed-plates of cast iron is rarely 
made a matter of calculation. To make it more than heavy 
enough and to dispose the metal in It in forms pleasing to the 
eye, which secures solidity and grace combined in a design, 
have been the objects which will be apparent from the study 
of successful practice. It is desired that the mass of metal 
in the bed-plate be sufficient to absorb by Its inertia the 
-effect of forces suddenly applied in the cylinder or suddenly 



2/2 MECHANICAL ENGINEERING OF POWER PLANTS. 




ENGINE FOUNDATIONS AND BED-PLATES. 273 

to be arrested at the crank-pin. The effect of these is hke a 
blow of some intensity, and there should be mass enough in 
the bed-plate to have it serve the purpose of an anvil. When 
there is sufficient mass in the bed-plate, it will absorb vibra- 
tions caused by unbalanced forces in action in the mechanism 
and prevent their reaching either the ground, the foundation, 
or the material by which they might be transmitted. If the 
bed-plate proper were of sufficient mass, the engine would not 
need to be secured to a massive foundation, but could stand 
on simple blocks adequate to support its weight. It is an old 
rule that the anvil should have a mass ten times that of the 
hammer-head which strikes on it. It is almost impossible to 
make the bed-plate of the stationary engine too massive. 

152. The Foundation of an Engine. — It is possible to 
make the bed-plate of an engine massive enough to make any 
other foundation unnecessary. It is not usual, however, to 
do this, because there are other purposes served by a proper 
foundation outside of that of absorbing the action of forces in 
the engine mechanism. Sometimes below the bed-plate 
proper a surbase of cast iron is used to which the bed-plate 
is bolted, and which in turn is secured to the foundation. It 
is more usual to have the bed-plate rest directly on the foun- 
dation. The functions of an engine-foundation are threefold. 

I. To support the concentrated weight of the engine upon 
the ground by distributing that weight over a sufficient area 
to prevent settling. Accepted figures for the supporting 
power of different soils are given in the following table : 

Alluvial soil. ... .... from .5 to i ton per square foot. 

Clay, soft '' I " 1.5 

dry '' 2 '' 4 

" thick '' 4 '' 6 

Sand, clean dry ** 2^4 

" compact *' 4 '' 8 

Gravel and coarse sand, from 4 to 8 tons per square foot if 

protected from water. 
Hard rock, up to 200 tons per square foot in thick strata. 



274 MECHANICAL ENGINEERING OF POWER PLANTS. 

If the soil is so unreliable as to require piling, crib work, 
and other artificial underpinning, the student is referred to 
text-books which make a specialty of foundations. 

2. The engine-foundation must go deep enough or far 
enough below the surface to be beyond the effects which cause 
unequal settling either from frost, vibrations, or the influence 
of loads borne by adjacent ground. The depth below the 
surface desirable for an engine-foundation will vary, but it is 
rarely safe to permit less than three feet of foundation below 
the general level. In excessive cold and in exposed situations 
the effect of frost will be felt down to six feet below the 
general level. 

3. The engine-foundation should have mass and weight 
sufficient to hold the engine still against unbalanced forces. 
It will be readily seen that in the case of a high-speed engine 
the weight of piston, rod, cross-head, and part of the con- 
necting-rod have to be started and stopped many times a 
minute. The pressure due to this comes upon the piston, 
but the cylinder-head and cover has an equal pressure to force 
it the other way. At the end of the stroke the living force 
of this same mass has to be arrested. This can be done 
by steam (pars. 88 and 90), or the crank-pin may have this 
work to do. If the steam does it, the reaction comes in the 
cylinder-cover and tends to slide it lengthwise; and if the 
crank-pin is to do it, it is desirable to balance the weights of 
these reciprocating parts by a weight opposite the crank-pin 
which shall provide for a storage of energy to be given out at 
the shaft in a direction opposite to that of the reciprocating 
parts and equalize their effect in jerking or jarring the shaft. 
The locomotive engine presents in its usual design a striking 
illustration of the counterbalancing of a reciprocating weight 
by a revolving weight between the spokes of its driving- 
wheels. It is possible by carefully proportioning the weight 
and acceleration which belong to the reciprocating parts to 
equalize in a great degree the shocks upon the crank-pin when 
the strains reverse, but a necessity for strength precludes the 
use of very light weights for these parts, and nearly all encrines 



ENGINE FOUNDATIONS AND BED-PLATES. 2/5 

are counterbalanced to secure quiet and steady running. The 
presence of the revolving counterbalance either in the crank 
or in the fly-\v^heel throws the engine-shaft out of balance, 
since there is weight on one side which has no equivalent 
weight symmetrical to it. While, therefore, the engine has 
been balanced in one direction, it has been thrown out of 
balance in the plane at right angles by reason of this 
counterbalance. The designer must therefore select in which 
plane he will have the engine balanced. In horizontal engines 
it is much more convenient to balance the engine in the hori- 
zontal plane, so that it shall have no tendency to slide length- 
wise upon its supports. By doing this with a revolving 
counterbalance there has been introduced a force which tends 
to lift the engine and cause it to vibrate up and down. The 
weight or mass of the foundation must be sufificient to hold 
the engine down against the action of such forces. In vertical 
engines the sliding tendency in a horizontal plane is also the 
one to be counterbalanced, and the foundation must absorb 
in such an engine the vertical forces which play in a plane 
parallel to the cylinder-axis (see par. 33). 

4. The engine-foundation must furnish sufficient mass 
to absorb vibration if the bed-plate is not massive enough 
to do it alone. The foundation being made up of masonry 
is easily and conveniently built up in place, while to make a 
massive casting would not only be more costly per cubic foot, 
but would make weights of such magnitude that handling 
would be troublesome. 

When the foundation rests on rock and is not suf^ciently 
massive it has been found that the vibrations caused by reac- 
tions in the engine are transmitted almost perfectly to the 
adjoining foundation upon the same rock. Great care has to 
be observed to attain success. 

153* Construction of Engine-foundations. — The founda- 
tions for very large engines will be of cut or dressed masonry 
according to the usual specifications for first-class masonry. 
Where the importance of the structure warrant it, tunnels or 
thoroughfares will be made or left through the mass of the 



2^6 MECHANICAL ENGINEERING OF POWER PLANTS. 

foundation by which access may be had to the lower ends of 
the bolts by which the bed-plate is bolted to the masonry 
(Fig. 230). 

For small engines, footings of rough masonry or ashlar 
may be used to distribute the pressure, and on this footing 
the foundation proper of brick will be built. The third plan 
is to make the foundation a monolith of concrete. Upon a 
proper footing to distribute the weight, a box of rough boards 
without top or bottom is laid, and within it successive layers 
of cement concrete are thrown in and well rammed until 
the desired height is reached. When brick is used it should 
be of first quality, hand-burned, and laid in cement-mortar. 
Common lime-mortar is liable to crumble and disintegrate 
under vibration, and the whole principle of the foundation is 
to have it act as a solid mass. When appearance is to be 
considered, the face of the brick foundation may be made of 
face or Philadelphia brick, while the interior is of ordinary 
grades. Since the bed-plate is to be bolted to the foundation, 
the greatest care must be observed in locating the necessary 
bolts in their proper places. 

154. Footings to Prevent Vibration.— The mass which it 
is convenient to get in a vertical engine bed-plate is often not 
enough to provide for the absorption of all vibration. The 
vertical engine, when chosen because floor-space is to be saved, 
does not call for extended area in the foundation, so that suffi- 
cient mass can only be gotten by going deep. Where this is 
inconvenient, or where rock is struck, engineers have had to 
provide special footings to arrest vibration. It has been tried 
by some to underlay the foundation proper with timber or 
rubber, but a springing material of a class to which these 
belong is often the occasion which causes the very difficulties 
they are designed to prevent. 

Vibration of machinery or any solid substance is of two 
sorts: the material either swings crosswise as in the vibrat- 
ing string of a musical instrument or in a flapping belt, or the 
motion of the particles is lengthwise or parallel to their long 
axis. If the oscillation or vibrating period of the material 



ENGINE FOUNDATIONS AND BED-PLATES. 2/7 




278 MECHANICAL ENGINEERING OE POWER PLANTS. 

used as an absorber of vibration happens to coincide with the 
vibration period caused in the engine-frame by the speed of 
reciprocation or by the belt-flap, the deadener partakes, and 
multipHes the objectionable vibration. What is to be sought 
to deaden vibration and arrest its transmission is some material 
to underlie the foundation which shall be without any resili- 
ence whatever. 

Probably no better material is to be found for the purpose 
of stopping vibration than sand, if it can be kept dry and 
all motion prevented, and the foundation-block itself is of 
sufficient mass. The foundation-pit is dug two or three feet 
deeper and two or three feet wider on all sides than the 
foundation proper is to be. This pit is surrounded with 
proper sheathing to prevent the displacement of the sand, 
which is filled in two or three feet below the bottom of the 
foundation, and then around it on the sides as it is built up. 
Hair-felt or mineral-wool layers have been used underneath 
the footing-course. If the foundation-block is not massive 
enough, these methods or expedients only aggravate the dif- 
ficulty which they are intended to cure. Very satisfactory 
results have been obtained abroad from the use of asphaltic 
concrete for massive footings. It possesses a certain sort of 
elasticity with its massive character, and its period of vibra- 
tion is so definite and so much shorter than the period of the 
engine's vibrations that the latter are broken up and neutral- 
ized before they reach the transmitting rock or hard-pan. 

Most annoying vibrations are caused in high-speed engines 
by the impact of steam in an exhaust-pipe with elbows. The 
difficulty is intensified when there are water or oil drops in the 
exhaust current. Their impact against the elbow which 
deflects them will set lengths of pipe atremble, and their 
motion will be transmitted over a very extensive area. 

155. Foundation-bolts. — The bed-plate requires to be 
strongly and stiffly secured to the foundation in order that 
the latter may act with the bed-plate as one mass, and to 
prevent the bed-plate from moving upon the foundation. 
These bolts will vary in size with the size of the engine, but 



ENGINE FOUNDATIONS AND BED-PLATES. 



279 



it is very undesirable to use bolts of such small diameter that 
it can be possible to twist them off with any ordinary wrench. 
Common diameters of bolts for engines of medium size would 
be from i-J to i^ inches diameter. The largest engines will 
require 2-inch bolts, but the smallest would use j-inch. The 
length of these bolts will be determined by convenience. It is 
desirable to have them go a good ways down into the founda^ 
tion, if not all the way to the bottom, in order that the upward 
strain upon them may be widely distributed in the founda- 
tion. 

The location of these bolts in the foundation must be 
determined by the holes in the bed-plate through which they 
have to pass. It will be seen by examining typical bed- 
plates that as a general rule there are bolts at the cylinder end^ 
or in the feet, and bolts at the crank-shaft end (Fig. 230), 
The bolts, furthermore, have to be built into the foundation. 




Fig. 231. 

and at such a height that when the foundation is completed, 
and the bed-plate placed upon it, the upper end of the bolts 
shall protrude through the holes in the bed-plate enough to 
take the nut which these upper ends are to carry. 

The method used to secure this object is shown in Fig. 231, 
which presents a typical arrangement for this purpose. The 



280 MECHANICAL ENGINEERING OF POWER PLANTS. 

wooden frame is called a template. It has holes made 
through it at points which correspond to the holes in the bed- 
plate, and when the nuts are in place on the upper end of the 
bolts the template is adjusted to the proper height above the 
datum plane, or plane of reference, and the foundation is built 
around the hanging bolts. The lower ends of the bolts are 
fitted with thread and nuts, on top of which rest the bearing 
or distributing plates or washers of cast or wrought iron. The 
distributing-plate is to enable the effort of the bolt to be borne 
by a number of bricks without danger of pulling through, and 
the nut and thread permit a vertical adjustment of the bear- 
ing-plate so that it shall come at the under surface of a joint 
in the coursed masonry. To permit of a certain limited 
horizontal adjustment of these foundation-bolts, several 
builders have surrounded the bolts with a length of pipe 
reaching from the bearing-plate to the top of the masonry. 
The diameter of this pipe is so chosen that the bolt can be 
deflected within the hole which the pipe makes^ and, after the 
bolt is in place and the alignment completed, the space be- 
tween the bolt and the pipe is filled with cement and the posi- 
tion of the bolt is fixed. The template in Fig. 231 shows 
the bolts required for the outer bearing of the engine-shaft 
attached to the principal template. This is usual when 
drawings of the template are furnished by the engine-builder 
and it is desired to make the foundation all in one piece. 
Where the length of the engine-shaft makes it desirable to 
have a separate foundation for this outer bearing it is usually 
more convenient to work with an independent template. 

156. Alignment of Foundation-template. — The founda- 
tion-bolts of the bed-plate will bear a certain relation to the 
axis of the cylinder. The axis of the cylinder should be in a 
plane truly at right angles with the axis of the engine-shaft. 
If the engine-shaft is to drive a line-shaft by belting or gear- 
ing, these two shafts should be truly parallel. Hence it is of 
prime importance to have the cylinder-axis perpendicular to 
the line of shafting, and the template which carries the bolts 
must be very carefully placed or oriented with respect to these 



ENGINE FOUNDATIONS AND BED-PLATES. 28 1 

determining lines. The drawing furnished by the builder of 
the engine from which the template is to be made usually has 
on it the centre-line of the cylinder, so that it can be laid out 
upon the boards of the template. 

For the obtaining of the vertical plane through the 
cylinder-axis a line stretched over the foundation-pit and 
carried to suspended plumb-bobs is the usual device. For 
laying off the centre-line of shafting or wall-lines the ex- 
pedient of snapping a chalk-line upon the floor is the most 
convenient. The centres of the shaft are transferred to the 
floor by plumb-lines, or offsets may be taken from permanent 
walls. Such centre-lines having been established, the plane 
at right angles to it is established by points and lines using 
either a transit with graduated horizontal limb and making 
repeated readings, or by the ordinary geometric methods, or 
by the use of a massive T square whose head and blade exceed 
six feet in length and whose squareness has been carefully 
verified. 

If a pulley or belt-wheel has been placed upon the line- 
shaft to which it is desired to draw a perpendicular line, a most 
convenient method is to stretch a twine or fine wire across 
the diameter of the pulley as nearly as the shaft will permit. 
With pulleys which have been turned, the edges of the face 
determine a plane perpendicular to the axis, so that the tense 
string touching the face at one point will only touch the face 
at a point on the other side of the shaft when the further end 
of the string lies in a plane which is perpendicular to the axis. 
This same method is a very convenient one to extend for the 
purpose of bringing two shafts parallel to each other where 
both carry pulleys. 

157. Locating the Bed-plate on the Foundation. — The 
foundation being completed, the bed-plate is to be lifted upon 
it and dropped into place with the bolts passing up through 
the holes in the bed-plate. Where cranes or similar lifting 
appliances are a feature of the power-house equipment this 
process becomes simple. In their absence the bed-plate must 
be lifted by jacks and blocking high enough to clear the bolts. 




282 MECHANICAL ENGINEERING OF POWER PLANTS. 

It must then be rolled on skids into place, and then lowered 
by the successive withdrawing of the blocking. 

The masons or bricklayers who have built the foundatioa 
do not usually have appliances for working to as close dimen- 
sions or as accurate levels as the setting of the engine 
requires. Furthermore, the top of the foundation is rarely a 
true plane, while the bottom of the bed-plate is very nearly a 
plane as a rule. It is necessary, therefore, to make a joint 
between the bed-plate and the masonry-work which shall 
support the bed-plate all over and in a plane as nearly level 
as it can be made. This process is so much easier when the 
brickwork or jointed masonry is covered by a single flat cap- 
stone, that where the dimensions of the foundation permit 
its use it will be preferred. It is usually a sawed or planed 
slab of bluestone or flagstone from 'four to six inches thick, 
and a little larger than the foundation-pier to which it serves 
as a finish or coping. The holes for the foundation-bolts have 
to be drilled in it, and it is lowered to its place upon a good 
bedding of cement. In the absence of such a cap or coping 
the bearing of the bed-plate comes upon a surface which is 
full of joints. The bed-plate is lowered over the foundation- 
bolts, and rests upon thin flat shims, or wedges of metal, which 
are placed on each side of the bolts between the bed-plate 
and the foundation. The nuts of the bolts are then screwed 
home, compressing the shims, while the bed-plate is carefully 
levelled as the strain is taken at each bolt. By driving in or 
loosening the shims any distortion or warping of the bed- 
plate by the bolts is prevented, and the bolts are tightened 
home until they refuse to go further. 

The bed-plate is now rigidly bolted to the foundation and 
rests upon a number of points in a plane. Between the bed- 
plate and the foundation is a place between the shims equal 
to their thickness, and this joint requires to be filled. The 
materials used for this purpose in setting a bed-plate and 
making the joint are five. They are methods applicable ta 
the setting of any machinery. 

I. Shredded oakum may be driven into the joint with a 



ENGINE FOUNDATIONS AND BED-PLATES. 283 

chisel, as the seams of wooden vessels used to be calked. 
This makes an elastic sort of joint, but it lacks permanency. 

2„ Felted hair is used in the same way and has the same 
properties. 

3. A rust-joint, as it is called, may be used. This is made 
by taking a thin cement-grout into which cast-iron borings or 
chips are introduced with a little powdered sal ammoniac 
and flour of sulphur. A dam of putty or clay is made around 
the outside of the bed-plate, and this mixture run into the 
joint and well worked in with a trowel. The rusting metal 
unites the mixture to the iron, and the cement to the stone. 

4. The sulphur-joint. This is one of the most widely 
used methods for bedding the engine. A clay or putty dam 
is made around the bed-plate, and the ordinary roll sulphur 
melted in an old kettle and poured into the joint between the 
bed and the masonry. It expands on solidification somewhat 
like ice to fill every interstice and give full support to the 
bed-plate. It undergoes no deterioration from oil or vibra- 
tion. If care is not taken in melting the sulphur, it will 
become too hot and begin to oxidize, giving off an irrespirable 
gas. Sulphur in melting becomes fluid at a comparatively 
low temperature, becomes more viscid as the temperature 
rises, and passes to a second fluidity just before it is ready to 
burn. 

5. The type-metal joint. Advantage is taken of the 
property possessed by certain antimony alloys (such as 
Babbitt, type-metal, etc.) of expanding at the moment of 
solidification to use them for bedding or jointing bed-plates. 
The method of using them is the same as that practised with 
sulphur, and they are preferred by many engineers particularly 
for bedding the narrow feet used with Corliss bed-plates. 

158. Alignment of Outer Pillow-block or Shaft-bearing. 
— It will have been observed in many of the engines which 
have been illustrated that the crank-shaft has a bearing on 
each side of the crank-pin and connecting-rod. Such engines 
are called centre-crank engines. The two bearings for the 
shaft are on the bed-plate, and the fly-wheels overhang their 



284 MECHANICAL ENGINEERING OF POWER PLANTS, 

bearings. Figs. 92, 93, and 229 illustrate engines of this type. 
Side-crank engines, on the other hand, have a shaft bearing 
behind one crank on the bed-plate, but the outer end of the 
shaft requires an independent bearing. The fly-wheel or belt- 
wheel or both will usually be upon the length of the shaft 
between these two bearings. (Fig. 226.) 

It will be seen at once that the location of this outei' 
bearing is of vital importance. In smaller engines it can be 
provided for approximately by the template as shown in Fig. 
231, but for large engines and for its final adjustments in small 
engines a different method should be used. 

If the outer bearing is too high or too low, it will force the 
crank to revolve in a plane making an angle with the true 
vertical plane, and twist the connecting-rod in each stroke. 
If out of place in a horizontal plane while correctly located in 
a vertical plane, it will force the crank to revolve in a plane 
which makes an angle with the axis of the cylinder, in which 
case it will bend the connecting-rod in each stroke; or it may 
be out of place in both planes, so that the connecting-rod will 
be both twisted and bent. The effect of either or both errors 
of alignment of this outer bearing is to wear the crank-pin out 
of its cylindrical shape, and to cause a knock or pound, and 
heating at the joint, which no adjustment of these bearings 
will cure. The proper method of aligning the outer bearing 
involves, first, the establishment of the true axis of the cylinder 
after the bed-plate is in place and the foundation-joint com- 
plete. This is best done by stretching a fine piano-wire 
through the empty cylinder, carefully adjusting it to the centre 
of the bore and fastening it tightly stretched to walls or fixed 
objects. To get the wire central is a matter of painstaking 
care and trial with gauges of wood or metal whose length is 
the cylinder-radius. The axis of the cylinder being estab- 
hshed, the shaft and crank are put in place in the bearing on 
the bed while the outer bearing is provisionally supported and 
located. The shaft is then turned until the crank coming 
towards its inner dead-centre touches the wire which marks 
the prolongation of the cylinder-axis. It will touch it at a 




ENGINE FOUNDATIONS AND BED-PLATES. 



285 



certain distance from the end of the crank-pin and from one 
of its collars. (Fig. 2.) The shaft is then turned over until 
the crank-pin approaching its outer dead-centre touches the 
wire. It will only touch it at an equal distance from its end 
or some fixed collar if the shaft is revolving around an axis 
truly at right angles to the wire. The outer bearing should 
be adjusted horizontally until the wire cuts the crank-pin at 
the same point and in the same plane on its outer and inner 
centres. 

The adjustment of the horizontal plane may be effected by 
a sensitive level if the engine has also been levelled in the 




Fig. 232. 

plane at right angles to the cylinder-axis in setting upon the 
foundation. A more sensitive and satisfactory vertical adjust- 
ment of the outer bearing is made by putting the crank-pin 
at 90° from its dead-centre, and holding a plumb-line so as to 
touch the wire at the pin, noting the distance of the vertical 
plane thus established from the end of the pin or a fixed collan 
If the plumb-line touching the wire also touches the crank- 
pin at the same distance from the reference-mark when the 
pin is at half-stroke below the wire, then the pin is turning 
in a vertical plane through the wire, and the outer bearing 
requires no vertical adjustment. 

Where adjustment is required the usual procedure is fol- 
lowed of correcting half the error and testing the alignment 
again. The outer pillow-block is often made to rest upon a 
special foundation-plate which has provision for the adjust- 



286 MECHANICAL ENGINEERING OF POWER PLANTS. 

ment upon it of the bearing proper in the horizontal plane 
{Fig 232). The vertical adjustment otherwise is made either 
by shimming or filling in with sulphur or type metal below 
the plate, and the last and finest adjustment can be made by 
liners underneath the bearing-brasses. The alignment of 
vertical engines is usually simpler than that of horizontal 
engines, because the bearings are always on the bed-plate and 
have been made right as to alignment by the builders in their 
shop-handling. The alignment in the erection of beam-en- 
gines is a sim.ple and obvious extension of the principles laid 
down above. The vertical cylinder-axis and the vertical 
through the centre of the crank-pin when the latter is at the 
top and at the bottom of its travel determine the vertical 
plane in which the beam must play, and the crank-pin at its 
90°. and 270° point must remain in that same plane. The 
alignment of engines afloat is so complicated by the motion 
of the hull that little use can be made of perpendiculars 
and horizontals, and the centre-lines must be deoended on 
entirely. 



CHAPTER XV. 

CYLINDER, PISTON, AND PISTON-ROD. 

159. The Cylinder-casting. — If the steam-engine is ex- 
posed to internal pressure from the steam radially in every 
direction along its length, the intensity of this radial pressure 
will be measured by the maximum steam-pressure throughout 
most of its length. At the ends, however, and against the 
heads the cylinder may be exposed to pressure much in excess 
of the steam-pressure from the presence of water. The 
intensity of the pressure due to water may be enormous. It 
will be apparent that as the piston nears the end of its stroke, 
the linkage of crank and connecting-rod forms the elements of 
an elbow-joint, and that the living force of the mass of metal 
revolving in the fly-wheel is exerted to straighten out this 
elbow-joint. If the water between the piston and the cylin- 
der-head would fill a volume in excess of the clearance, it will 
be apparent that its incompressibility makes it act like a solid 
mass of wood or metal and transmit to the cylinder the entire 
effort of the straightening elbow-joint. If the metal is strong 
enough to hold, the engine will be stopped, or some yielding 
at the joints or bending of the mechanism may permit the 
crank to get past its centre. For this reason, because the 
actual strain on the cylinder is scarcely susceptible of calcula- 
tion, the thickness of metal to be* used in the cylinder is fixed 
rather on the basis of experience, by the condition of stiffness 
against deformation, and to be thick enough to permit of 
reboring when worn. 

The metal to be used for a cast-iron cylinder should be a 
uniform close-grained iron having a certain hardness or ability 

287 



288 MECHANICAL ENGINEERING OE POWER PLANTS, 

to resist abrasion. Experience in mixing irons in the foundry 
is of great use in this respect, and excellent results have been 
obtained from the use of an iron containing manganese. This 
metal seems to give a smooth or slippery surface to smooth 
abrasion, while working easily under the pointed cutting-tools. 

The casting of the cylinder is either made all in one piece 
with the massive bed-plate or it is bolted to it. When made 
in one piece, as is usual in engines of the Tangye bed-plate 
patter.n, a joint is avoided at the crank end of the cylinder, 
and no difficulty is to be experienced from the cylinder shifting 
its alignment with the bed. On the other hand, the finishing 
of that end of the cylinder is made more difificult. In Fig. 
162, which represents a bolted cylinder, there will be observed 
radial set-screws attached to the flange on the crank-head, 
whose function it is to secure and adjust the alignment of the 
cylinder and the bed-plate. 

The cover of the cylinder is bolted to the cylinder proper 
by means of a series of studs, whose inner end is tapped into 
the flange or solid metal of the cylinder, and whose outer ends 
carry nuts by which the cover is held steam-tight to its place.. 
The joint between the cylinder and the cover is a ground or 
metal and metal joint and requires no packing, or at most a 
gasket of oiled paper. Many designers use a cross-section of 
the studs so that in case of entrapped water the stretch of 
these bolts within their elastic limit shall open the joint 
enough to release the water. These cylinder-covers are often 
cracked across by water, and precautions must be taken to 
prevent such accidents. The cover is usuall}" so modelled on 
the inside as to enter the bore of the cylinder and help to 
reduce the waste room or clearance. While Fig. 162 shows 
the head covered with a false plate, it is easily seen that the 
head might be cast with hollow recesses in it in which steam 
can be circulated to prevent heat-losses, as in Figs. 146, 163, 
and 167. 

The cylinder should be bored in the shop in the position 
in which it is to work. That is, a vertical cylinder should be 
bored on end, and a horizontal cylinder on its side. The 



CYLINDER, PISTON, AND PISTON ROD. 289 

reason for this is that the weight of the metal in the cyl- 
inder will distort it while the boring-tool develops a true cyl- 
inder. The cylinder which was bored vertically will sag and 
shorten the vertical axis when laid on its side, while the cyl- 
inder bored horizontally under strain of its own weight will go 
out of round when stood up on end so that the weight is 
taken off. 

The valve-chest is usually cast on the cylinder and in one 
piece with it so as to avoid joints. It may be on the top on 
one side or both sides or on the bottom. It will be con- 
structed with a convenient lid or bonnet so that access can be 
easily had to valves and seats for examination or repairs. 
The nuts on all studs of covers, lids, and bonnets will be care- 
fully case-hardened to prevent injury from wrenches. And 
it is best to use only fixed spanners accurately fitted to such. 
nuts in order to avoid mutilating the corners. Such wrenches 
and spanners accompany every well-made engine. 

160. The Counterbore. — By reference to Fig. 162 it will 
be observed that the bore of the cylinder at its two ends is 
slightly larger than the standard diameter through the rest of 
its length. This enlargement of the bore is called the coun- 
terbore, and its object is threefold. 

I. The piston in its motion should slide up to and beyond 
the end of that part of the cylinder on which the piston bears. 
In other words, it must traverse the entire length of the 
cylinder-bore proper. Without this precaution the pressure 
of the piston or its rings, wearing the bore up to a certain 
point only, will develop a shoulder at that point, and any 
change in the length of the connection between the piston 
and crank-pin caused by wear will make the piston bring up 
against this shoulder at one end or the other and cause a 
knock or pound. If the piston laps over into the counter- 
bore at each stroke, it wears the whole length equally and no 
shoulders should occur. 

2. The slight enlargement simplifies the operation of get- 
ting in elastic rings such as are fitted to most pistons to make 
them steam-tight. 




290 MECHANICAL ENGINEERING OF POWER PLANTS. 

3. The counterbore, undergoing no wear in use, serves as 
a truly cylindrical surface to re-establish the axis of the 
cylinder for reboring in case of wear. 

The counterbore and the steam-passages into the cylin- 
der should be so related to each other and to the bore proper 
of the cylinder that the pressure of steam entering the 
cylinder should not come upon the piston sidewise, but from 
the end. If this detail is disregarded, the steam-pressure will 
at admission drive the piston against the opposite side of the 
bore and cause a disagreeable knock or pound. This will be 
worse at the head end, because the rod is more flexible. It 
is mitigated by prolonging the piston-rod out through the 
head. 

161, Cylinder-cocks and Snifting-valves. — To drain the 
cylinder and to get rid of excessive water of condensation, a 
hole is drilled into each counterbore at the lowest point of 
the cylinder, into which a pipe-connection is tapped. These 
drain-pipes are controlled by valves, and discharge either into 
a closed tank, or into the condenser or a drain, or simply into 
the open air, as may be convenient. The valves are called 
cylinder-cocks, and will be opened when the cylinder is to be 
warmed at starting, or when it gives indications of excessive 
water by the noise of snapping or cracking, like a hammer- 
blow, which is the indication of its presence. In large cylin- 
ders, which will be weak to resist the action of water, and in 
marine engines, where the pitching and tossing of the boilers 
may cause abnormal quantities of water to come over with the 
steam, automatic relief-valves are provided to open of them- 
selves in such an emergency. These snifting-valves are 
usually plain conical valves opening outwards, and held in 
place by a coiled or flat spring. The tension of such a spring 
is made greater than the usual steam-pressure, so that in 
normal conditions they remain on their seats. Excessive 
pressure from water lifts them off their seats against the spring 
and relieves the cylinder and its cover. P'ig. 233 shows two 
types of relief-valves and a form of breaking cap. A special 
brass fitting screws into the cylinder, and has a thin plate 



CYLINDER, PISTON, AND PISTON-ROD. 



291 



soldered over the large opening, but not too strongly. The 
plate is easily renewed if forced out by excess of water. 

162. The Cylinder-jacket or Lagging. — The radiation of 
heat from the cylinder must be reduced as far as possible. 
This is desirable, first, to diminish condensation of steam 
which ought to do work in the cylinder, and, second, to keep 
the engine-room cool. Furthermore, the doing of work in the 
cylinder by expansion condenses a certain weight of steam 




Fig. 233. 

and it becomes desirable to diminish internal waste in the 
cylinder from re-evaporation of such condensed steam as far 
as possible. For this purpose the walls of the cylinder are 
often cast hollow so that live steam from the boiler can circu- 
late through these hollow passages and keep the working bore 
hot. This hot steam surrounds the working bore, and the 



292 MECHANICAL ENGINEERING OF POWER PLANTS. 

appliance to keep it there is called a steam-jacket. Fig. 18 r 
shows the steam-jacket and cylinder, and Fig. 162 shows the 
valve-chest thus jacketed. The constructive difficulty of the 
hollow bore comes from the unequal expansion of the outer 
and the inner wall in cooling. This makes the inner wall very 
liable to crack in service in large engines. The difficulty has 
been met in two ways. First, by making the bore of the 
cylinder an inner lining which fits in properly prepared 
shoulders or flanges in the outer casing which forms the 
jacket. The joint between the lining and the rest of the cast- 
ing is made by copper rings. The cylinder-cover closes down 
upon this lining to prevent displacement. The other plan is, 
not to make the jacket a continuous casting, but to have its 
two halves united by an expansion-ring of some flexible metal 
which will make the joint steam-tight, but will yield to 
changes of length (Fig. 234). 




LEAVITT JOINT. CORLISS JOI NT-. 

Fig. 234. 

Outside of the jacket, or protecting the cylinder-casting 
proper if there is no jacket, is a provision for some non-con- 
ducting material. This may be hair-felt, mineral wool, or 
wood, or combinations of these with asbestos board. This 
non-conducting material may be held in place either by narrow 
strips of wood, or by thin staves of cast-iron, or by a sheathing 
of Russia sheet iron. This is called a lagging. The choice 
of method will be fixed by the taste of the designer, and it 
may be em.bellished by the use of polished rings. Its object 



CYLINDER, PISTON, AND PISTON-ROD. 293 

is to prevent radiation and at the same time to produce a 
pleasing effect to the eye (Fig. 166). 

163. The Structure of the Piston. — The piston is to fit 
the bore steam-tight. It must therefore have sufficient area 
of contact with the bore to bear efficiently and to accommo- 
date the packing devices. It is therefore not calculated as a 
rule, but receives a length which is the result of experience in 
the main. By reason of its size it would have unnecessary 
weight in large engines if made solid, and for the sake of 
lightness it is usually to be met in one of three forms. 

1. The solid piston, vvhich is usual in small engines only. 

2. The box piston. In this the two faces of the piston 
are of solid metal, but the spaces between them are made 
hollow by the use of cores, in casting, having the shape of a 
sector of a cylinder. Such cores form the piston into a series 
of internal chambers separated from each other by partitions 
which form stiffening ribs to prevent the piston from being 
forced out of shape. These cores, which form the chambers, 
are supported upon feet of their own material which will 
leave holes in one or the other face out through which the 
material of the core is withdrawn. These holes in the face 
are then tapped, a plug is screwed in to refusal, and the 
metal of the plug cut off. The hollow where the core has 
been is at first filled with air only, but water or oil is apt to 
Avork through the pores of the iron into the cavity more or 

• less. Some ugly accidents have happened from the heating 
of old pistons without a previous venting of these cavities. 
An accumulated pressure from air or gas heated to a high 
tension has rent the piston in pieces. 

3. The spider-and-follower piston. In this the piston is 
made in two pieces or more. The solid part, called the 
spider, consists of one face and the side or contact surface. 
This cup or dish-shaped part contains the centre hub to which 
the rod is attached, and from it to the sides radiate ribs which 
give stiffness and strength. It is these radiating ribs from 
the central body or hub which give it the name of spider. 
The other face of the piston is a separate plate which bolts to 



294 MECHANICAL ENGINEERING OF POWER PLANTS. 

the ribs or hollow of the spider and forms the cover. It is 
called the follower. When the follower, instead of forming; 
the entire face, is merely a ring rather than a plate, it some- 
times retains its older name of junk-ring. It received this 
name when the packing material was hemp or junk and access 
was had to the grooves in which this junk was packed by the 
removal of the ring. In most cases the follower-plate comes 
off the piston or spider on the side opposite the piston-rod. 
An exception is met in beam-engines, where the piston-rod 




Fig. 235. 

goes out through the top of a vertical cylinder. Convenience 
of access from the top induces the follower plate or ring to be 
on the piston-rod side in this case. The follower plate or ring' 
is fastened to the spider by bolts which are themselves made 
of bronze, or their nuts are. The object of this practice is to 
prevent the nuts rusting fast to the thread and refusing to 
come off. The piston in most cases is made of cast-iron. 
This is because of the convenience of shaping and fitting, but 
furthermore because it is desirable that the piston and cylin- 
der-bore should be of the same metal or of equal hardness. 



CYLINDER, PISTON, AND PISTON-ROD. 



295 



Recently some locomotive pistons have been made of steel 
disks and of aluminium or other bronzes, for the sake of 
lio-htness; but when steel is used a cast-iron outer shell has 
often been fitted which forms the contact-surface with the 
cylinder and carries the packing appliances. It is likely that 
steel and strong metal-plate pistons will come more and more 
into use. 

In vertical engines it is common to round the upper 
face of the piston or to make it convex, while the lower cylin- 
der-head is made similarly convex upwards and the lower face 
of the piston correspondingly concave. The object of thus 
doming these surfaces is to cause them to shed water outward 

J 




Fig. 236. 

from the centre to the bore so that it will pass into the 
exhaust-passages and the drip. 

Figs. 146 and 163 show the typical solid piston; -Figs. 
235, 162, and man)^ others, typical box or hollow pistons; 
and Fig. 236, the usual form of follower piston used in loco- 
motives. Fig. 237 shows the new type of steel-plate piston. 

164. The Piston-packing. — The piston cannot ordinaril}^ 
be fitted to its bore so as to be steam-tight. This is, first, 
because the piston and the bore are fitted cold and will 
expand unequally when heated. If the bore expands more 
than the piston, it leaks. If the piston expands more than 



296 MECHANICAL ENGINEERING OF POWER PLANTS. 

the bore, it is seized by the latter too tightly to be moved if 
it was a close fit when cold. Furthermore, wear of the con- 
tact-surfaces would make a solid piston fit loosely in the bore 
after a certain time and permit leakage. If the piston leaks, 
steam passes directly from the inlet to the exhaust-pipe, and 
so to waste without doing work. This increases the consump- 
tion of steam per horse-power and the consumption of coal. 
For such reasons some form of packing appliance to make 
a steam-tight joint and allow for expansion and wear has been 
used from the beginning. 

In the first steam-engines made, before the machine tool 




Fig. 237. 

known as the boring-machine had been invented, the cylinder 
was cast as nearly, cylindrical as possible and smoothed by 
hand. A joint between the piston and the cylinder was made 
by coiling a plaited square gasket of hemp-fibre or junk into 
a wide groove formed in the piston. This gasket was made 
of an eio;ht-strand braid, and was held in place and forced out- 



CYLINDER, PISTON, AND PISTON-ROD, 29/ 

wards by screwing down the follower-plate or junk-rIng (hence 
the name). These elastic or fibrous packings were adequate 
for low pressures and low temperatures, such as prevailed in 
the early days. They can still be used for water-packings, 
and combinations of canvas and r-ubber may still be used 
under conditions of this sort. What is known as the cup 
leather packing has also to be used with cold flu-ids. An 
annular ring of leather, having an exterior diameter greater 
than that of the bore, is pressed into the bore when wet so as 
to turn cup-shape, and is drawn up against the piston and held 
in place by a ring acting just like a junk-ring. The cup of 
the leather ring or disk which lies against the bore is pressed 
outwards by the pressure of the fluid, and leakage is pre- 
vented. 

The only way in which pistons can be made tight without 
packing-devices is by the use of what is called leakage- 
grooves. These are a series of shallow grooves turned in the 
sides or bearing-areas of the piston and so numerous that the 
pressure leaking from one groove to the next shall not have 
time to establish itself in all of the grooves and pass from the 
last into the exhaust side during a period occupied by one 
stroke. The principle is that pressure must be fully estab- 
lished in the first groove before steam will leak from the first 
groove through the narrow space between the piston and bore 
into the second groove, and so on. Such pistons would not 
be tight if they stood still or moved at low velocity. At high 
speeds they serve their purpose if there are enough grooves, 
but their presence makes the piston of unusual length in the 
direction of its motion. The grooves become filled also with 
the lubricating material, and with water of condensation, 
which helps to make the joint tight. They have less friction 
than elastic packing. 

165. Piston-rings. — By far the most usual method of 
making a piston steam-tight is by means of rings which fit 
in grooves turned in the bearing-surface of the piston. It is 
intended that these rings shall fit their grooves on their sides 
closely enough to prevent leakage around them, and that they 



298 MECHANICAL ENGINEERING OF POWER PLANTS. 



shall be forced radially outwards with sufficient force to pre- 
vent steam leakage between them and the bore. Such rings 
are called piston packing-rings, and they will differ with 
different designs according to their material, according to 
their number, and according to the metal used to keep them 
tight against the bore. 

The materials used for piston-rings are cast iron, steel, 
and composite metals. The advantages of cast iron are, first, 
its cheapness; second, that it has the same hardness as the 
bore and so does not wear it unduly; and third, its conveni- 
ent elasticity. 

The advantages of steel are its elasticity and that it is not 
as fragile as cast-iron rings. Cast iron has been known ta 
break from shock or vibration while in service and cause 
unpleasant consequences in the cylinder. The use of steel 
rings for pistons is attributed to Ramsbottam of England. 

The composite rings are brass or bronze rings, or rings of 
such metal in which recesses are cast and in which recesses 
some soft bearing metal like babbitt is cast to form the. contact 
with the cylinder-bore. The object of these composite rings is. 
to obtain a bearing metal softer than the bore, so that the wear 
shall be concentrated upon the rings, which are easy to renew. 
The objection to the steel rings is that they are likely to 



1 




Fig. 238. 

abrade the cylinder by their superior hardness or density, and 
to rebore the cylinder is more troublesome and expensive 
than to renew a worn-out ring. 

The ring in order to be elastic must be a non-continuous 
ring, or with a break at some point in order that its length 
may vary. This joint between the two ends of the ring mus^t 
be prevented from allowing a leak. This is done either by 
simply making the joint a scarf-joint, or by fitting a tongue- 



CYLINDER, PISTON, AND PISTON-ROD. 299 

piece which shall slip in the ring at one end while fastened 
in the other and thus close the joint (Fig. 238). It is very 
usual to have two rings, so that the joints in the two rings 
may be on opposite sides of the piston. Fig. 235 shows the 
rings in separate grooves, while Fig. 162 shows two rings in 
the same groove. 

To press or force packing- rings radially outward against 
the bore, five methods are usual. 

1. To depend on the elasticity of the ring itself. This is 
applicable to pistons up to 16 or 20 inches in diameter, but 
is not desirable for larger sizes. It is used both with steel 
and cast-iron rings. The ring is turned as a solid ring to fit 
a diameter larger than the bore. Usually the proportion is 
a quarter of an inch larger for each foot of diameter. The 
finished ring is then sawed apart and sufficient metal taken 
out at the joint to permit the ring to be squeezed together so 
as to enter the cylinder. It will tend to expand to its orig- 
inal size against the restraining bore, and this pressure makes 
a steam-tight joint. Such rings are called snap-rings. They 
do not guide the piston at all, as they are loose in the grooves 
sufficiently to move freely, but not enough to leak. To keep 
the radial pressure of the ring against the bore the same at 
every point so as not to wear the cylinder unequally, the 
thickness of the ring should be graduated and should be 
different at different distances from the joint. 

2. The packing-ring proper of cast iron and steel is forced 
outwards by an inner or spring ring. This is a common plan 
in large vertical engines where the weight of the piston does 
not come upon the rings or springs. It can also be used in 
horizontal engines of medium size (Fig. 162). 

3. Flat springs, pushing the rings radially outwards at sev- 
eral points of the circumference. This is a favorite locomotive 
design and for larger horizontal engines (Fig. 236). The flat 
springs can be adjusted by nuts or screws to give greater or 
less tension, and in horizontal engines with heavy pistons the 
tension on the lower springs may properly be made greater 
than on the upper. This type is applicable, only to pistons 



300 MECHANICAL ENGINEERING OF POWER PLANTS. 

of the follower type, and the adjusting of the springs requires 
that the follower be removable. In vertical engines these 
springs should all be set out equally, and a clever design by 




Scale= 



Fig. 239. 

Mr. W. F. Durfee is shown in Fig. 238, where the adjusting- 
studs bear upon a conical surface so that they are all set out 
or relaxed by adjusting the cone from without. 



CYLINDER, PISTON, AND PISTON-ROD. 



301 



4. The packing-ring may be forced outwards by positive 
means, such as screws or wedges or combinations of them. 
The idea is that with a true bore there is no occasion for 
elastic pressure upon the packing-ring, but that it causes 
unnecessary friction. If the ring is set out just enoug-h not 
to leak, and the bearing-contact of the ring and bore is large 
enough, there is no occasion forgive or take in the ring. The 
wedge or screw is variously applied, either to enlarge the 
diameter of a split ring by separating its ends or by pressure 
exerted radially upon the packing-ring or the inner bull- or 
junk-ring. This type of packing is applicable, of course, to 
follower-pistons only. 

5. Steam packing. Fig. 240 shows a plate piston packed 
with two rings. The groove behind each ring is connected 




Fig. 240. 

at several points through small holes with the steam-pressure 
acting on the piston, so that the packing-ring is forced out- 
wards by an elastic pressure of steam behind it. It is usual 
but not necessary to make these packing-rings in segments 
which overlap each other so as to prevent leakage at the 
joints, whereby the steam-pressure does not have to overcome 
any resistance in the metal of the ring in forcing it out. 
When steam is shut off, the steam-spring ceases its action and 
lessens the friction in the cylinder. This form of packing 
was first associated in America with the name of Dunbar and 
has been much used. 

A modification of the principle of steam piston-packing 
has been ingeniously applied in some large horizontal engines 
with a view to diminish the friction of the piston and its ten- 



302 MECHANICAL ENGINEERING OF POWER PLANTS. 

dency to wear the bottom of the cyHnder. Steam is admitted 
through a hollow piston-rod to a place on the bottom of the 
piston, extending like a groove part way around its bottom 
surface. The area of this groove is calculated so that with 
the usual steam-pressure the upward reaction of the steam in 
it- which comes from the hollow rod shall just balance the 
weight of the piston. Rings prevent the steam from leaking 
out of the groove, and in normal conditions the piston should 
slide upon a layer of steam and without metallic contact with 
the bore, so as to be nearly frictionless. 

l66. The Piston-rod. — The piston-rod has to transmit 
the motion of the piston to the mechanism outside of the 
cylinder. It has to withstand both push and pull, and the 
former without bending. It is rarely massive enough to 
have no tendency to bend with the weight of the piston when 
the latter is at the head end of horizontal engines. If calcu- 
lated as a pillar for compression, it will be abundantly strong 
to resist tension provided that it be properly secured in the 
piston. The piston-rod has also to withstand the tendency 
to abrasion or to wear out of round where it passes through 
the cylinder-head and its stufifing-box. For these reasons a 
great many piston-rods are made of high-carbon steel which 
has been treated by the process known as cold-rolling, which 
gives it a particularly dense, hard, and close texture on the 
outside, and so increases the modulus of elasticity as to in- 
crease its resistance to bending from the weight of the piston. 
The usual methods for fastening the piston-rod to the piston 
are five. 

1. The piston-rod is threaded and the piston screwed on 
it with a thin jam-nut or set-screw, to prevent unscrewing 
(Fig. 237). 

2. The piston-rod is formed with a shoulder, and between 
the shoulder and the end a straight or tapering surface which 
ends in a screw-thread is turned. The piston is bored to fit 
the straight or tapering end of the rod, and when the rod is 
in place the thread on the rod protrudes enough to take a 
strong nut. The collar and the taper surface take the push 



CYLINDER, PISTON, AND PISTON-ROD. 303 

of the piston, and the nut takes the pull. These methods 
have the advantages of being cheap, and the joints between 
the piston and rod are easily broken (Figs. 162, 181, 240). 

The objection to the second plan is that the projecting 
nut requires that a clearance be made for it (see Figs. 162, 239), 
and there is always a possibility that the screw-joint exposed 
to push and pull will in time work the nut downward along 
the threads so that the joint becomes loose. When this 
happens it makes a knock or pound which is hard to locate. 
The nut is liable to corrosion in the cylinder and to rust to its 
threads. Where it may be expected or desired that the 
joint between piston and rod is to be frequently broken, the 
nut may be made of a bronze alloy. 

3. The taper is drawn in by a key of metal (Fig. 236). 
The end of the rod is formed into a tapering or conical sur- 
face which fits a corresponding hole in the piston. A rectan- 
gular slot is cut at right angles to the axis of the rod, and a 
similar one across the hole in the piston. These slots are so 
related to each other lengthwise that a rectangular key driven 
through the slot when the rod is in place shall bear in the 
piston upon the end nearest the large base of the cone, and in 
the rod upon the end nearest to the small base. The driving 
in of the key draws in the male cone of the rod into the 
female cone of the piston with a very strong pressure until 
the key refuses to be driven farther. 

This method is an elegant one, but is applicable to fol- 
lower-pistons only. The key is within the hollow part of this 
piston, it entails no clearance, it is very strong, and the joint 
between piston and rod can be easily loosed if necessary. 
This is done by the use of a special offset key driven after 
the original key has been removed, and which reverses the 
pressure by which the piston was drawn on the rod, by having 
its bearing upon the opposite ends upon the slot in each. 
The objection to it is its cost and the possibility of the joint 
working loose from a slacking off of the key. There is not 
much weight in these objections. The taper of the rod may 
be either i in 32 or i in 64, according to the amount of force 



304 MECHANICAL ENGINEERING OF POWER PLANTS. 

with which it is desirable to draw the one cone over the 
other. 

4. Riveted rods. The end of the rod with collar or taper 
surface fits the piston and projects slightly through it. The 
projecting end is then upset and turned back upon itself as 
a rivet is headed. Such riveting of the rod may be done hot 
or cold. If done hot, the rod in shrinking as it cools draws 
the piston more tightly against the shoulder or the taper. 
The heat may injure or scale the surface of the rod. The 
advantages of this method are that it is cheap and tight and 
takes no room. The joint cannot be broken without destroy- 
ing the rod. It is a favorite joint in small cheap engines, 
where the value of the rod is so slight as not to warrant the 
cost of an expensive joint. The cold-riveting of the rod does 
not injure the rod by scaling, and can easily be made tight 
against the least motion. The head of the riveted rod is 
often formed in a cup-shaped depression or countersink. 

5. Shrinkage-joints. This is a very elegant joint for pis- 
tons of medium size. The hole in the piston which is to take 
the rod is made straight and cylindrical, but is smaller than 
the diameter of the rod in the proportion of .0025 of an inch 
for each inch of such diameter. This makes a hundredth of 
an inch for a four-inch rod. The piston is then heated to 
low redness, whereby the hole is expanded sufficiently to 
permit the rod to enter it. As it cools it contracts upon the 
rod, and seizes it with a pressure so great and firm that the 
rod will part somewhere in its length before the piston will 
slip off. The advantages of this joint are its tightness; it can 
be broken by heating the piston while the rod is kept cool; 
it involves no clearance. The objections to it are its demand 
for exact working to dimensions if it is to succeed, and the 
strain on the piston and the effect of heat upon it. This 
method of making joints by shrinkage is often used about the 
crank for its shaft and pin with the same advantages. 

In follower-pistons the joint with the rod is often designed 
so that the follower-plate shall cover over it and remove any 
necessity for clearance in the cover. 



CYLINDER, PISTON, AND PISTON-ROD. 305 

The front end of the rod is to be secured to the cross- 
head. This must be a joint easily to be taken apart, since 
the cross-head must be put on after the piston and rod are 
in place in the cylinder. It will therefore be found that much 
the most usual plans are to thread this outer end of the rod 
and screw it into the cross-head with a jam-nut to prevent 
unscrewing; or to taper the end of the rod and the hole in 
the cross-head, and draw them together with a transverse 
key. The screw plan will be used on small and medium-sized 
engines, and the key on medium-sized and large. Figs. 260 
to 266 will serve to illustrate typical methods of securing the 
rod to the cross-head. 

167. The Stuffing-box. — The hole through which the pis- 
ton-rod must pass steam-tight through the head requires to be 
fitted with special devices to prevent leakage. As in the case 
of the piston, the rod must be surrounded by an elastic and 
adjustable material which shall permit the rod to pass in and 
out with the least friction, and which yet shall seize it tightly 
enough to prevent leakage of steam when the pressure is on 
and prevent the entraining of water with the outward motion 
of the rod on the exhaust-stroke by a sort of a capillary action. 
The combination which is used for this purpose is called a 
stuffing-box. It consists of a sort of cylindrical box or 
cavity, the packing proper which goes into that box, and the 
gland by which the packing is compressed and held in place. 
There must also be a method for tightening and holding the 
gland. 

The typical stuffing-box is exhibited in Figs. 162 and 165. 
It is quite usual where the rod enters the bottom of the 
stuffing-box to force a bronze annular bushing into the hole 
in the cylinder-head so as to make the rod fit this bushing 
quite closely. The advantage of the bushing is that it can be 
easily forced out and replaced when it becomes inconveniently 
worn. It is preferable to have the softer bushing worn by the 
rod rather than to have the more costly rod worn by the harder 
metal of the cylinder-head. The bottom of the stuffing-box 
cavity tapers inwards towards the rod, and the inner end of 



306 MECHANICAL ENGINEERING OF POWER PLANTS. 

the gland likewise. The effect of this is to produce a com- 
ponent inwards against the rod when the gland brings pressure 
parallel to the rod, and thus to compress the contents of the 
stuf^ng-box inwards upon the rod. Fig. 162 shows the gland 
drawn inwards by two stud-bolts. This is a most usual plan 
with rods of medium size. For small rods such as valve-stems 
the arrangement shown in the same figure and in Fig. 165 is 
more usual because of the room which is required for bolts of 
practical size. For such small rods the outside of the stuffing- 
box, instead of being formed into a flange, is threaded, and a 
hollow nut fitting over the gland will draw the latter inwards 
when screwed upon this stuffing-box thread. This is the usual 
method for valve-stems and similar small rods. For large rods 
above four or five inches in diameter two bolts are not 
enough to draw the gland symmetrically inwards and prevent 
it from cocking or binding sidewise, which would cause great 
friction and wear. Care must be taken to prevent this in any 
case, but with very large rods requiring four or six bolts in 
the stuffing-box, as in marine practice, the nuts are often 
made into small pinions or gears which work into one large 
gear so that the turning of one turns all the bolts at once, as 
in the self-centring chuck. This difficulty is avoided when 
the gland-nut is used. 

For the packing material to be used in the stufifing-box 
the qualities to be sought are elasticity and low coefficient 
of friction, absence of abrasive effect upon the rod, and 
capacity to prevent and absorb leakage. Early packing 
materials were hemp and cotton-fibre plaited into gaskets and 
laid in loosely. More recently combinations of cotton in the 
form of canvas with rubber have been much used. The 
rubber gives elasticity, the canvas the quality of absorbing 
and holding the lubricant. The lubricant not only diminishes 
but opposes the passage of water. Paper-fibre also has been 
popular. Packings of this class are laid in the stuffing-box 
in a spiral coil, the thickness of the packing material being 
standardized to standard dimensions of the space in the 
stuffing-box which the packing is to fill. Packings of one- 



CYLINDER, PISTON, AND PISTON-KOD. 



307 



half, five-eighths, or three-quarter inch thickness will be usual 
in engines of medium size. 

The objections to these fibrous and rubber packings are 
iirst encountered with high pressures of steam, and secondly 




Fig. 245. 

"with high heats. Oxidation and abrasion of the fibre under 
pressure and heat and a hardening of the rubber under heat 
make it necessary to renew the packings frequently, and they 
have but a relatively short life of entire tightness. This 
trouble is particularly present in vertical engines with the 



308 MECHANICAL ENGINEERING OF POWER PLANTS. 



piston coming out of the bottom of the cylinder. Unless the 
packing be excessively compressed so as to cause undue fric- 




FiG. 246. 
tion, the rod will draw water out with it past the packing by 
a sort of capillary action. Combinations of asbestos-fibre^ 



CYLINDER, PISTON, AND PISTON-ROD. 



309 



which is not affected by heat, have given great satisfaction in 
stuffing-boxes, but exceeding care must be used, both in 
manufacture and in use, that there be no hard or gritty par- 
ticles of the mineral. Where care is not taken the rod 
becomes fluted or scored lengthwise from the abrasive action 
of such hard spots. 




Fig. 247. 

To make a more mechanical method of packing which 
should last longer and resist both heat and pressure, a wide 
variety of metallic packings has been made. The principle 
of such packings is to have a series of split rings whose 
exterior surfaces slope alternately from and towards the rod, 
so that when endwise compression is exerted by the gland 
they close inward upon it. Sometimes a coiled spring is in- 
troduced behind the gland, so that the compression of the 
split rings may be an elastic force instead of a positive and 



3iO MECHANICAL ENGINEERING OF POWER PLANTS. 

unyielding compression. Furthermore, such rings are often 
arranged so as not to fill the stuffing-box space sidewise, but 
to admit a certain give-and-take if the rod and the axis of the 
cylinder should not happen to coincide perfectly. The most 
striking illustration of this will be found in the method of 
construction in the Straight Line engine, Fig. 167. Here the 
packing is really a long cylinder which has a motion around 
a spherical joint in the end of the cylinder to permit of adjust- 
ing its own alignment. 

Certain forms of metallic packing are shown in Figs. 245,. 
246, and 247. If the piston-rod is to project through the 
back head, a stuffing-box is also required there; but it is of 
less importance if the path traversed by that projecting rod 
is inclosed in a steam-tight cylinder which it fits nearly tight. 
Provision must be made, however, in this case to get rid of 
water which may accumulate there from leakage. 

168. Air-valves. — In engines of the locomotive class 
where the mechanism of the engine may be expected to run 
on for considerable periods after steam is shut off, provision 
must be made to guard against the pumping action of the 
piston in the cylinders. The continual exhausting of the con- 
tents of the cylinder makes an inward pressure, and dirt, cin- 
ders, and other foreign matter would thus be drawn in. This 
difficulty is met by having a valve opening inward attached 
to the steam-chest which will be shut upon its seat when 
pressure is on the valve, but will open by atmospheric pressure 
and let clean air enter when the pressure falls below atmos- 
phere. Fig. 164 shows the principle of these air- valves upon 
a locomotive valve-chest. 



CHAPTER XVI. 
CROSS-HEAD GUIDES AND CONNECTING ROD. 

169. The Guides or Slides. — The cross-head gets its 
name from the fact that it is the head of the piston-rod, and 
as ordinarily constructed it forms a T or cross-shaped head to 
such rod. The cross-head and the guides which control its 
motion are counterparts or complements of each other, and 
the form, number, and arrangement of guides will be depend- 
ent on the preferred arrangement of the cross-head. 

The condition which the guides must fulfil is that of 
keeping the end of the piston-rod from bending out of the 
axis of the cylinder when the strain on the connecting-rod 
produces such a tendency. The plane or planes of the guides 
must therefore be truly parallel to the prolonged axis of the 
cylinder, and it is the convenience of securing such parallelism 
by means of the level which makes it so desirable that the 
engine bed-plate and the cylindeu-axis should be truly hori- 
zontal upon the foundation. In many forms of bed-plates 
the guides are formed and finished in the bed-plate casting 
and at the same setting of the tool at which the cylinder is 
bored. This insures a common axis for cylinder and guides. 
Where the guides are loose and need to be set up on the bed- 
plate great care must be exercised in their alignment. 

When the fine-wire axis is established (par. 158), this is 
best done by means of special fixed gauges or trammels. In 
the absence of such appliances the ordinary surface-gauge, or 
better the micrometer surface-gauge, may be used. When 
one guide or one pair has been made parallel to the axis, the 
other guide or pair should be made absolutely parallel to the 
first. To have the alignme^it of the guides defective is to 

3" 



312 MECHANICAL ENGINEERING OF POWER PLANTS, 



invite wearing at the stuffing-box and wearing of the bore of 
the cylinder out of round, and to cause unnecessary friction 
and often a knock or pound in the engine which is hard to 
locate. 

The guides may control the cross-head by action in a 
vertical plane or in a horizontal plane. They may be in 
number, one, two, or four. Their surfaces are exposed to 
abrasive wear, and they should be massive enough or so shaped 






M" 



vf 



m m 



-44- 



^ 



h-4-M 



ii ^ 



ttJ5 



l-iffs 



■-4 



-53-1/2— 



-9'/s- 



•^-f 




Fig. 260. 
or supported as to resist the tendency to deflect. To resist 
abrasion they are often case-hardened, and to resist deflection 
they are often made thicker as the distance from the support- 
ing ends increases. 

Where but one guide is used it will appear in one of two 
forms. In the first form the cross-head will be arranged to 
embrace the rectangular guide on all four sides with the 
piston-rod and cross-head pin in the plane of the guide and 



CROSS-HEAD GUIDES AND CONNECTING-ROD. 



313 




SH MECHANICAL ENGINEERING OE POWER PLANTS. 

below it. The cross-head pin must be far enough below the 
guide (Fig. 260) so that the swing of the connecting-rod at its 
widest amplitude shall clear it. This form of cross-head is 
used quite a little in locomotive practice, but care must be 
taken that it should be long enough not to cock or bind upon 
its guide. This is likely to occur with short cross-heads of any 
form if the line of the resultants due to the reaction of the 
connecting-rod on the pin passes at any time outside of the 
centre of the pin, or even near the edge of the bearing surface. 
The other form of single guide is sometimes known as the 
guide for the slipper cross-head, and is shown in Fig. 261. 
The engine in this case must turn in one direction only, and 
the guide is a flat plane surface with suitable edge's to prevent 
sidewise motion of the cross-head. Fig. 261 shows also a 
convenient method for adjusting the plane of the guide in 
case of wear of the rubbing surfaces. This form is very easy 
to lubricate. 

When two guides are used they may either embrace the 
cross-head if the guides are in the plane in which the connect- 
ing-rod oscillates, or the cross-head must embrace them if they 
are in the plane at right angles to that in which the connect- 
ing-rod oscillates. If there are four guides, they will embrace 
the cross-head in either arrangement. This must lead to the 
discussion of the cross-head. 

170. The Cross-head. — The cross-head for a single guide 
has been already discussed. With two guides it is much more 
usual to arrange them to guide a vertical cross-head, which is 
one guided in the plane in which the connecting-rod oscil- 
lates. With this arrangement the guides must be far enough 
apart to clear the connecting-rod in the angle just before, half- 
stroke, when it departs furthest from the cylinde-r-axis. This 
makes the cross-head of sufficient extent laterally to meet the 
contact-surface. With such vertical cross-heads the guides , 
may be flat and plane (Fig. 262), they may be cylindrical (Fig. 
263), or they may be each in two planes inclined to each other 
(Fig. 264). The great advantage of the cylindrical guiding 
surface (Fig. 263) is that the cylinder and guides are so con- 



CROSS-HEAD GUIDES AND CONNECTING-ROD. 



315 



venlently bored at one mounting with a boring-bar having two 
cutting heads. This secures coincidence of the axis of cylin- 
der and guides. The objection to it is that there is nothing 
to prevent a twisting action except the attachment of the 
connecting-rod to the crank-pin. It is a very usual method 
in relatively small engines. With any of these cylindrical 
cross-heads the guide-surfaces usually are moulded and finished 
in the solid metal of the bed, and the adjustment for wear 
and for symmetry with the cylinder-axis under wear is affected 
by adjustments in the cross-head itself. The contact-surface 
of the cross-head is usually made by special metal pieces which 
are called gibs. These gibs may be simply cast-iron shoes, 
cast-iron shoes with recesses for babbitt or other bearing- 
metal, bronze shoes, or shoes of some wood well calculated to 
resist abrasion, such as lignum vitae. The principle of these 




Fig. 262. 

gibs is that they shall concentrate upon themselves the wear 
and shall be cheaply renewable. They should furthermore 
have a low coefficient of friction. These gibs being detached 
from the solid metal of the cross-head can easily be made to 
be adjustable in the plane at right angles to the cylinder-axis 



3l6 MECHANICAL ENGINEERING OF POIVER PLANTS. 



by means of screws or wedges or bolts. Fig. 262 shows the 
adjustment by means of lateral wedges, and Fig. 264 the adjust- 
ment by longitudinal inclined planes. In early Corliss cross- 





FiG. 263. 

heads the central part was attached to the shoes or gibs by. 
bolts of some diameter which were separately adjustable and 





Fig. 264. 

held by jam-nuts when the adjustment was complete. A 
simple type for small engines is often met in which an occa- 



CROSS-HEAD GUIDES AND CONNECTING-ROD. 31/ 

sional variation can be made by having the adjustment-bolt 
fixed in position, while washers or liners of thin metal or even 
of paper are taken out of the space between the collar and 
the gib as wear or adjustment may require. 

The cross-head using two guides in the plane at right 
angles to the oscillation of the connecting-rod has the cross- 
head embrace the guide on three sides with gib adjustment. 
This is a usual adjustment in beam-engines such as Fig. 
30. The gibs are like those shown in Fig. 260; but as they 
will be on the outside of the guides, their adjustment 
becomes very simple by the use of screws passing through the 
solid metal of the cross-head and embedding slightly in the 
gib. This can also be used on the vertical cross- head, but is 
not considered so satisfactory and mechanical an arrange- 
ment. Nearly all inverted vertical engines are guided in the 
plane of the connecting-rod when they have an A frame, or 
else make use of the slipper one-guide cross-head when they 
have open frames as in Figs. 15, 17, and 53. 

The four-guide cross-head has been a favorite form for 
locomotive practice and in much stationary practice. It 
makes a comparatively light cross-head, and yet the contact-^ 
surface is abundant and generous. The two guides on each 
side of the connecting-rod can come as close together as con- 
venient instead of having to be at a determinate distance 
apart. Fig. 266 will show the general appearance of a cross- 
head of this type, which has the further advantage that by 
generous bearing-areas the pressure per square inch may be 
so far reduced that no appreciable wear is to be expected 
during the lifetime of the engine, thus simplifying the con- 
struction of the cross-head, doing away with gibs and their 
appurtenai:ices. The slipper cross-head has this same advan- 
tage. Where gibs are thought desirable they can be easily 
introduced, or wear may be taken up by the introduction 
or removal of liners of thin paper under the blocks which 
separate the guides at their ends. If the contact-pressure be 
kept below 40 pounds per square inch of area, and a proper 
lubricant kept continuously supplied, a thin film of oil will be 



3l8 MECHANICAL ENGINEERING OF POWER PLANTS. 

always separating the surfaces, and if they never touch they 
never wear. Care must be taken that the design of the cross- 
head prevents the resultant of pressures ever passing outside 




Fig. 266. 

of the contact-surface. If it does, there will be a tendency 
for the cross-head to cock or press a corner down upon the 
guides, scraping off the oil and setting up abrasive wear. It 
is best to have the pin on which the connecting-rod swings in 
the centre of the length of the cross-head for this reason. 
The gibs, furthermore, should have grooves cut diagonally or 
zigzag fashion in their contact-surface to hold the oil and 
distribute it sidewise over every element of the guide. It 
will be apparent that the lower guide needs to be lubricated 
in a horizontal engine which throws over, and the upper 
guide or upper gib in an engine which throws under (Fig. 3). 
The resultant of alternate push and pull is always in one 
direction for the engine which turns in the same direction. 



CROSS-HEAD GUIDES AND CONNECTING-ROD. 319 

171. The Cross-head Pin or Wrist-pin. — The connect- 
ing-rod requires a pin on which to oscillate while transmitting 
its motion to the crank. It is usual to make this pin fast in 
the cross-head and have the connecting-rod swing on it. 
This, however, can be reversed if necessary. The cross-head 
must transmit the effort to the connecting-rod through the 
axis of the piston-rod and the connecting-rod. Hence the 
wrist-pin must either be borne in a hollow in the cross-head 
or, if the cross-head is solid, the connecting-rod must have a 
forked end and take hold of the pin on each side of the cross- 
head. There are objections to this latter plan, to be dis- 
cussed hereafter, so that it is most usual to support the pin 
so as to have it in double shear. In vertical cross-heads 
the pin is apt to be made a tapering fit in its hole so as to be 
drawn to a tight bearing by its nut. A small key also is' 
used in addition to prevent turning (Fig. 264). In horizontal 
cross-heads the pin is usually inserted from above into a 
proper slot. The guides and a steel bolt through the guides 
keep it from displacement It is usual to make the wrist- 
pin hollow in order that oil may be introduced through 
the centre, and so out by a radial hole to the contact-surface. 
In the Porter wrist-pin the surfaces outside of the sector of 
steam effort are flattened away so as to form an oil-cellar from 
which the surface of the connecting-rod will continually draw 
oil upon working surfaces. 

172. Parallel Motions.— In beam-engines, where the guide 
for the cross-head can only be secured by braces to the frame, 
which makes their alignment troublesome and uncertain, it 
has been quite usual to dispense with guides, and to control 
the cross-head by means of jointed linkages. These linkages 
are so designed and proportioned that the motion of the cross- 
head is compelled to be in a straight line, either exactly or 
so very nearly that the error is inappreciable. Such linkages 
are called parallel motions. The best known are Watt's, 
Evans', Russell's, and the. Peaucellier cell. Their use is 
restricted in modern practice to a very narrow scope, and the 



320 MECHANICAL ENGINEERING OF POWER PLANTS. 

student is referred to treatises on kinematics for a discussion 
of their properties. 

173. The Connecting-rod. — The connecting-rod in the 
typical engine mechanism must transmit the alternate push 
and pull of the steam effort to the revolving crank-pin. It 
must furthermore withstand the tendency to bend transversely 
due to the flinging effect caused by its own weight or mass 
as it passes the half-stroke point and has its transverse motion 
suddenly changed. Furthermore, its bearings at the two ends 
are exposed to friction and wear, since the entire pressure on 
the piston must be borne upon the relatively small areas of 
the pins, and the crank-pin rubs its contact-surface in the con- 
necting-rod through a space equal to its own circumference in 
one revolution and under the pressure due to the steam. It 
will be apparent that the flinging strain will be greatest with a 
long rod and at high rotative speeds. The rubbing difficulty 
will be greatest with high pressures and large diameters, and 
the wear greatest with high rotative speeds. 

The cross-section of the connecting-rod to meet these 
requirements is in most cases an elliptical or oval, or even an 
elongated rectangle with rounded top and bottom having the 
longer axis in the plane of motion. Lengthwise the greatest 
section is either put at the middle or in more modern prac- 
tice it is gradually tapered from the cross-head to the crank 
(Fig. 261). Flinging effect is zero at the cross-head pin and 
is greatest at a point just behind the crank-pin, or more 
properly at the radius of gyration of the rod. In very 
long connecting-rods, such as are used in river-boat practice 
East and West, the connecting-rod (here often called a pit- 
man) is braced by a king-post trussing of wrought-iron rods 
whereby strength to push and pull is fully retained and yet a 
much lighter rod results than would be the case if stiffness 
were sought by a solid deep rod (Fig. 11), A recent sec- 
tion of steel rod which has become much used in locomotive 
practice where the conditions for the connecting-rods are 
very severe is the I-shape section, in which the two flanges 
give strength against deflection and all unnecessary metal 



CROSS-HEAD GUIDES AND CONNECTING-ROD. 321 

and weight are withdrawn which would bend the rod (Fig. 
272). 

The effort of the rod is to deflect the cross-head sidewise. 
The shorter it is the worse this dif^culty. With a connecting- 
rod of infinite length there is no tendency to bend the cross- 
head and piston-rod. Ordinarily for practical reasons the 
connecting-rod will be two and a half to three times the 
length of the crank. It will be apparent that a connecting- 
rod of finite length introduces an irregularity into the motion 
of the piston. The piston has moved through more than half- 
stroke outgoing when the crank is at 90° from its dead-centre, 
and on the return from the outer dead-centre it has not moved 
through half-stroke at the 270° point. These irregularities 
afTect the accelerating of the reciprocating parts, but in ordi- 
nary cases are masked by the fly-wheel and by the steam-dis- 
tribution. 

174. The Stub End. — In order to provide for the concen- 
trated strain on the crank-pins and cross-head pins of engines 
an especial appliance has become nearly universal. The pins 
are usually of steel, carefully hardened in best practice, and it 
is desirable that they should not wear by abrasion, but that 
if wear must occur it should be concentrated upon the surfaces 
which bear upon these pins, rather than on the pins them- 
selves. Furthermore, the construction of these bearing-sur- 
faces should be such that wear may be easily taken up tO' 
prevent lost motion or pounding, and that when worn they 
may be easily and cheaply refitted or replaced. These con- 
ditions have brought about the combination of brasses, strap, 
gib and key, or cotter and wedge which is known as the stub 
end of the connecting-rod. 

The brasses are two half-cylinders which embrace the pin 
and form the bearing. They are called brasses when made 
of bronze (copper-tin alloys) as is usual, and even if made of 
cast iron. They may either be true bronze bearings, or they 
may be made with recesses into which Babbitt or other bear- 
ing metal is cast to form the actual contact-surface. The 
special purposes served by the brass or bronze bearing are, 



322 MECHANICAL ENGINEERING OF POWER PLANTS. 

first, that it is easily cast and tooled ; second, it is softer than 
the steel pin, and the wear will be concentrated upon it; 
third, it has a low coefficient of friction in case lubrication 
should become defective; fourth, it has a high conductivity 
for heat, and so draws heat of friction from the pins. 

In marine practice, and elsewhere where it would be incon- 
venient or impossible to stop, spare brasses can be kept on 
hand to replace that which must be allowed to wear itself out; 
and the replacing of such worn brasses is not a matter of shop 
repairs, but can be made by simply taking down the joint. 

The brasses should touch each other at the point which 
divides the bearing in two halves. As the bearing wears and 
lost motion begins, the brasses should be filed or scraped down 
until the wear or lost motion is taken up. Another plan is 
to have the joint open a little when the two half-bearings are 
in place and fill the gap with liners of thin sheet metal so that 
the bearing can be made solid. As the bearing-surfaces wear, 
these liners are successively taken out until the joint comes 
brass and brass, when refitting is necessary. Not to fill the 
opening between the brasses is to invite a cramping of the 
bearing upon the pin with friction heating and all attendant 
difficulties. In some locomotive practice in the past the 
brasses have been capped so as to encase the crank-pin com- 
pletely and keep dust out. 

The end of the connecting-rod proper bears against the 
outside of one brass while the other is drawn against the first 
half by a U-shaped forging called the strap (right-hand end 
of Fig. 270). The strap is carefully adjusted to the brasses 




Fig. 270. 

and the connecting-rod end, and is held in place and to its 
work by the combination which is known as the gib and key, 
or cotter. From Fig. 270 it will be seen that the gib and key 



CROSS-HEAD GUIDES AND CONNECTING-ROD 323 

in this form of stub are counterparts and form compensating 
inclined planes. As the key slides along the gib, the width at 
any section is increased. If then the gib and key be fitted in 
slots in the connecting-rod body and in the strap so that the 
key rests against the outer edge of the slot in the connecting- 
rod, the effect of driving down the key will be to draw the 
strap back, since the gib bears upon the strap, but is free from 
the inner end of the connecting-rod slot. By drawing back 
the strap, the joint in the brasses closes together and the key 
refuses to drive. A set-screw keeps the key from sliding out, 
and a solid construction results which is nevertheless easily 
removable and adjustable. 

It will be apparent that as the brasses wear in the form of 
stub shown, and the key is driven down, the effective length 
of the connecting=rod shortens. In time also the slots in 
the strap and rod end will come to match, and the key will 
drive no farther. This difficulty will be met either by 
renewing the brasses altogether or by fitting in between the 
rod end and the inner brass liners or shims of sheet metal 
which will move the centre of the bearing outwards as much 
as the wear has shifted it inwards. The form of stub shown 
in Fig. 270 is called an open stub. If open stubs are used 
at both ends of a connecting-rod, its effective length is 
shortened at the two ends by driving in the keys. 

It is called a closed stub when the gib or key bears against 
the inner brass directly, with the end of the rod as its abut- 
ment bearing-surface. Fig. 271 shows this construction using 
a wedge instead of a gib and key. As the wedge is adjusted 
inwards the inner brass moves towards the outer and away 
from the centre. The closed stub thus lengthens the rod to 
take up wear. If a closed stub is used at one end and an 
open stub at the other the distance between crank-pin and 
piston is varied by the difference in wear at the two joints; 
and if there is no difference in this wear, the length of the 
mechanism remains constant. This plan is much the most 
usual and to be preferred. The closed stub may be applied 
either to a rod whose end is forged solid (Fig. 270), or the 



324 MECHANICAL ENGINEERING OF POWER PLANTS. 



strap may be strongly bolted or braced and bolted as shown in 
Fig. 271. The wedges which are much used in modern en- 
gines for setting up brasses are 
operated by screws and are fully 
shown in the illustration. To 
prevent the loosening of keys 
in large engines and at high 
speeds, where the set-screw 
would not be enough, the end 
of the key is sometimes drawn 
down to a rod and threaded. 
A nut on this rod bears upon 
a Z-shaped bracket bolted to 
the rod and holds the key in 
place. It is the trouble arising 
from slinging of the key which 
has caused the wedge with its 
bolt to receive preference in 
modern usage. Fig. 272 shows 
a stub of this type, and illus- 
trates also the I section of the 
rod. A form of stub first in- 
troduced in marine practice is 
1 1 ..j J II shown in Fig. 273. The gib- 

L \ and-key construction is aban- 

y I doned, and the half-brasses are 

' ' held together in a jaw by bolts 

parallel to the length of the 
rod. These bolts have to with- 
stand the push and pull of the 
rod, but they make a very stiff 
and strong stub particularly well 
adapted for crank-pins of con- 
siderable length. They are also 
the foundation for very deep connecting-rods made of hollow 
tubes for compression, while through-bolts resist the tension 
as they hold down the outer halves of the brasses (Fig. 14). 




CROSS-HEAD GUIDES AND CONNECTING-RODS. 325 

Another form of stub is known as the round-end stub. The 
end of the connecting-rod has a tapering hole within which 
is inserted a bronze bushing which fits the taper on its outside 
and the cylindrical pin on its inner side. As wear takes 
place, the split in the bushing is filed out, and the bushing 
forced a little farther into the taper hole whereby it is closed 





Fig. 272. 

together. This is particularly adapted for parallel rods and 
side rods of locomotives, where it is necessary that the length 
between the centres should always remain the same. With 
the gib-and-key plan one end of such side rods had to have 
double keys, one outside the brasses and one inside. Some- 
times this cylindrical bushing plan is used without a split and 
provision for adjustment. When wear has become enough 
to be annoying, the worn bushing is thrown out and a new 
one put in place In light rods with small pins the solid eye 
is sometimes split, a little metal sawed out, and the split 
held from opening by a bolt. As the bearing wears, tighten- 
ing of the bolt closes up the slit and takes up lost motion. 
An interesting provision for taking up wear with ordinary 



326 MECHANICAL ENGINEERING OF POWER PLANTS, 






CROSS-HEAD GUIDES AND CONNECTING-RODS. 32/ 

brasses is shown in Fig. 274. A cavity behind the inner 
brass is filled with steel balls, and into that cavity a set-screw 
projects. The balls displaced by the screw press the brasses 
outward, and yet are practically immovable from an outer 
force. They act like the particles of a fluid to exert equal 
pressure upon the brass. This device is the invention of Mr. 
C. W. Hunt. 

175. Forked-end Connecting-rod. Double Rods. — 
When it is convenient or necessary to have the cross-head pin 
supported at its middle and to have the motion taken off 
symmetrically on each side of the axis of the piston-rod, the 
connecting-rod end may be formed into a sort of rounded Y 
with a bearing on each arm. This bearing will be of the 
usual stub construction, with provision for taking up wear 
(Fig. 15). The difficulties and objection to this forked-end 
construction are those which result when the two bearings wear 
unequally. The consequence of unequal wear is that one side 
or the other draws the farther end of the rod to one side and 
against the collars of the crank-pin when it is keyed up after 
refitting. The strength of the connection may be enough to 
keep the rod continually out of straight, causing friction, heat- 
ing, and wear. The only proper way to treat such a forked rod 
after refitting is to take off the crank-pin strap and brasses and, 
with the brasses of the fork keyed up close, test the alignment 
of the naked end of the connecting-rod with the crank-pin at 
the inner and outer centre. If it does not fall in line with 
the pin, liners must be introduced behind the brass on the 
short side, if it is an open stub, until the alignment is perfect. 
Forked-end connecting-rods are usual with the main connect- 
ing-rods of beam-engines, where they are made necessary by 
the support of the pin by a single beam. The use of a double 
beam with the pin between them makes this construction 
unnecessary. 

The symmetrical connection of the cross-head of a beam- 
engine to the central beam of such engines would compel a 
connecting-rod forked at both ends. This would be trouble- 
some and difficult, and for this reason it will be found that it 



328 MECHANICAL ENGINEERING OF FOWER FLA NTS. 

is usual to use two short connecting-rods for this purpose. 
Each has two stub ends, and the same difficulty attaching to 
unequal wear requires to be guarded against here. Unequal 
lengths of these rods springs the cross-head, twists the beam, 
and gives general trouble. The same difficulty is to be 
guarded against in engines of the back-acting type for blow- 
ing or pumping, such as shown in Figs. 13 and 14, where the 
connecting-rods are attached to crank-pins outside of the fly- 
wheel from the wide cross-head. So critical is this difficulty 
from unequal length of two similar connecting-rods that the 
proper construction for such a case is to have the cross-head 
merely pinned to a boss on the rod so that it may yield and 
adjust itself to such slight inequalities of length. Many 
massive cross-heads have been cracked from inattention to 
this detail. 

Small connecting-rods which can be hollow are frequently 
arranged to have a key at one end or even in the middle 
set up the brasses at both ends. A rod which passes 
through the hole in the bore bears against the brass at one 
end and against the key at the other. The term pitman 
sometimes applied to a connecting-rod should be limited to 
either a massive or long connecting-rod or to the connecting- 
rod which couples a vibrating beam or treadle to a revolving 
crank. The latter is its proper use, but it has been sanctioned 
by usage as a name for those wooden rods, stiffened by iron 
forgings on top and bottom, which are used as connecting- 
rods for the marine engines of the Western rivers. The mining 
origin of the term has been already referred to (par. 11). 



CHAPTER XVII. 
CRANK-SHAFT. ECCENTRIC. FLY-WHEEL. 

176. The Crank-shaft. — The power of the cyhnder is to 
be delivered in continuous rotary motion. The crank-shaft, 
therefore, requires to be one upon which the crank shall 
deliver the effort of the connecting-rod, and which shall carry 
the fly-wheel for regulating inequalities of effort and resist- 
ance; and if the power cannot be taken off from the fly-wheel, 
it must also carry the wheel or pulley or drum required for 
this purpose. Two great classes of crank-shafts are usual for 
single-cylinder engines or tandem compounds. They might 
be called single- and double-crank arrangements, but are more 
usually known as centre- and side-crank arrangements. In the 
side-crank arrangement the crank-pin projects from one side 
of the crank and is exposed to shearing in one plane. The 
bearing close to the crank will be on the frame, but the bear- 
ing on the other side of the fly-wheel will be independent. 
In the centre-crank or double-crank arrangement the crank-pin 
is between two cranks, and there is a bearing for the crank- 
shaft on each side of the connecting-rod upon the bed-plate 
of the engine. In this type there is usually no outboard 
bearing, but two fly-wheels, or two belt-wheels to be used as 
fly-wheels, overhang the bearings on the bed. Fig. 228 shows 
the arrangement of side-crank engines, and Fig. 229 the 
arrangement of centre cranks. 

When there are several cylinders side by side the arrange- 
ment of the crank-shaft must conform to this condition. For 
the ordinary cross-compound engine where the power is taken 
off from a central fly-band-wheel, as in Fig. 95, the cranks 

329 



330 MECHANICAL ENGINEERING OF POWER PLANTS. 



will overhang. In marine engines the cranks must be double, 
and generally the double crank makes the strongest arrange- 
ment. Fig. 280 shows the single overhung crank, and Fig. 
281 the double cranks for a triple engine. 





177. The Crank-pin. — The crank-pin is usually of high- 
carbon steel. It requires to be very solidly inserted into the 
eye of the crank, and to this end three methods are usual. 
First, it may be forced in by a press. The hole in the eye is 
made cylindrical, and the end of the pin which enters the eye 
receives a very slight taper at the very end, but the cylindrical 



CRANK-SHAFT. ECCENTRIC. FLY-WHEEL. 



331 



contact is practically of the same size in the eye and the pin. 
The pin is then coated with white lead and forced into the hole, 
which is a little too small for it. This is done either by 
hydraulic or screw presses exerting a force of 20 or 30 tons. 
The second method is to shrink the crank upon the pin by 
the method described in par. 166. The third plan is to have 
the pin and the hole taper, while the inner end of the pin is 
finished into a screw-thread on which fits a nut by which the 
tapers are drawn together. In some forms of disk-crank the 
pin may be held with a key. It is very usual to model the 





F= 


i "^f--.__ 




_ 


1 ± . 1 




Fig. 282. 

crank-pin with collars to prevent sidewise displacement of the 
brass of the connecting-rod upon it. On the other hand, many 
crank-pins are made without collars, and the shape of the 
brass keeps the connecting-rod from the plane of the crank,, 
and a plate which bolts to the end of the pin forms a finish 
which the eye seems to demand, and keeps the connecting-rod 
from appearing to slip off. When collars are used it is com- 
mon to fillet the corners rather than to give them a sharp 
angle where they join the bearing surface. The pin is not 
only stronger, but there is less danger of a binding of the 
brasses. 



332 MECHANICAL ENGINEERING OF POWER PLANTS, 

178. The Crank. — Whether single or double, cranks may 
be of cast iron or wrought iron or of steel. Since the shaft 
must be of wrought iron or steel, the continuous crank which 
is made in one piece with it, must be of the same metal. The 
cast-iron crank is therefore limited to cases where the shaft is 
built up. The ordinary form of cast-iron crank is shown in 
Fig. 282. Such crank requires to be secured to its shaft by 
means of steel keys inserted partly in the shaft and partly in 
the hub of the crank. It is usually more convenient to make 
use of two keys than to try to get sufficient shearing area in 
one. A much more usual form of the cast-iron crank is the 



Fig. 283 

disk-crank, such as shoAvn in Fig. 228. This arrangement 
permits of balancing the weight of the crank itself on the 
other side of the centre of motion, and furthermore gives a 
convenient space for additional metal which may serve to 
counterbalance the living force of the reciprocating parts. 
At high speeds, moreover, the disk-crank meets less resistance 
from the air. Where the disk-crank is not used in vertical 
engines a form of balanced crank, such as shown in Fig. 283, 
will be required to offset the weight or unbalanced effect of 
the mechanism. Some designers have built up cast-iron 
counterweights upon a wrought-iron crank. Fig. 284 shows 
an arrangement of this sort. 

When there are two cylinders to work upon one crank- 
shaft and it is to be a continuous or double crank, the double 
crank will be forged solid if the length of the stroke is not too 
great. The excess of metal will be cut out by slotting, and 



CRANK-SHAFT. ECCENTRIC. FLY-WHEEL. 333 

then the oin turned by mounting the shaft eccentrically in 




a lathe of sufficient size. Of course it is not easy to forge 
such cranks with short distance between them, nor is it easy 



334 MECHANICAL ENGINEERING OF POWER PLANTS. 

to get them truly at right angles. Built-up crank-shafts, 
where the crank-pins and lengths of shafting are separate or 
fastened together by shrinking and keying, have been much 
used in marine practice (Fig. 285). 







STEEL CRANKSHAFT, S.S. "ALASKA' 

Constructed by Messrs. Jol>n Elder & Co. 




CRANKSHAFT, "CtTY OF ROME^ 

Conatrudted of Whiteuorths Fluid Pressed Steel, 

Fig. 285. 



Section thrpugk AiBu 



179. The Locomotive Crank and Shaft.^ — The ordinary 
American locomotive is constructed so as to be what is called 
outside-connected. The cylinders and driving mechanism 
are outside of the frames, and the crank-pins are inserted into 
proper bosses in the driving-wheels. Inside-connected engines, 
with the cylinders and mechanism between the frames, require 
cranked axles and have no pins on the drivers. The inside- 
connected designs have been most popular in Europe by reason, 
of a supposed steadiness and because the effect of torsion 
between the two cylinders is exerted on a less 'length of axle. 
The cranked axle is, however, more difficult to forge. The 
inconvenience of having the principal parts of the mechanism 
clustered together under the hot boiler and between the 
frames, and the possibility of equal steadiness for the outside- 
connected design, have given the latter the preference in 



CRANK-SHAFT. ECCENTRIC. FLY-WHEEL, 335 

America. The driving-wheels are pressed on the axle by 
heavy hydraulic pressure, and twisting is prevented by keys. 
The crank-pin is also pressed into its boss. Where the length 
of the engine permits, the connecting-rod or main driving- 
rod acts upon the crank-pin of the main or forward driver. 
In short engines the connecting-rod will go to the rear 
driver. In the first case the main pin will have two bear- 
ing-surfaces on it, that for the main rod being nearer the 
face of the wheel. In the latter case the main-rod bearing 
will be outside of the. bearing for the parallel or side rod. 
Where there are three drivers on a side the main bearing will 
be outside, and the side rod connecting the main to the front 
driver will require a pin-joint near the main stub so that no 
cross-strain shall be brought upon it from inequalities of level 
in the track. Locomotive crank-pins seem to undergo a 
structural change from the combined effect of vibration and 
shock to which they are subjected, so that it is a custom to 
force them out after a certain number of miles have been run 
and have them forged over and replaced, to prevent a sudden 
breakage on the road with its attendant disaster. 

l8o. The Marine Crank-shaft. — For the ordinary paddle- 
wheel service in deep Eastern waters the crank is a double 
one, forged, and built up with inserted pin. The two halves 
are essentially alike, and with bearings close to the crank in 
the main frame and within and without the wheel. In a 
very few cases the two halves of the double crank are not 
in the same plane, but one is slightly behind the other in an 
offset eye. The object of this is to diminish the considerable 
danger in all long-crank engines lest the crank settle down 
upon the lower centre by the action of the waves upon the 
propelling wheels when the engine is at rest, which makes it 
troublesome to start. In Western river-boat practice with 
side wheels the shaft is usually not continuous across the hull, 
but the two engines are separate and are separately handled. 
This gives greater manoeuvring power in currents and for 
landing. Some special ferry-boats for railway service have 
also been constructed in this way. For marine engines which 



33^ MECHANICAL ENGINEERING OF POWER PLANTS. 



drive propellers at the stern it is apparent that the entire 
energy which propels the vessel must find an abutment against 
the lengthvvdse thrust of the screw in the construction of the 
shaft itself. This is done by means of what is called the thrust- 
bearing. This consists of a large bearing in which a sufficient 





^ 



xtr 



d" 







number of grooves or rings is formed which fit correspond- 
ing collars upon the shaft. The area of these collars and 
their number are proportioned to the energy for which they 
must provide, and the contact-surfaces in the bearing are very 
carefully fitted with Babbitt or similar bearing metal. These 



CRANK-SHAFT. ECCENTRIC. ELY-WHEEL. 33/ 

bearings are also cored so that circulation of water can be 
provided to keep them cool. These thrust-bearings are 
usually placed close behind the engine, so as to be always 
under the careful scrutiny of those running the engine. As 
the engine will be located as a rule near the centre of gravity 
of the hull, there will have to be a number of joints in the 
propelling shaft both for convenience of manufacture and for 
convenience of handling and repair. These sections will be 
joined by flanges carefully and strongly bolted together. Fig. 
286 shows the construction of the thrust-shaft and propeller 
section of a marine engine, and Fig. 287 the provision made 
at the stern to permit the shaft to pass outwards through the 
hull. The joint is made water-tight by means of stuffing- 
boxes, and the actual bearing of the shaft is upon lignum 
vitae or similar bearing material. Such shafts of large diameter 
are apt to be made hollow in best modern practice in order 
to secure strength with lightness and to eliminate the defects 
which in solid forging are apt to concentrate themselves at 
the centre both of the ingot and of the forging which results 
from it. 

181. The Main or Crank Bearing. — The bearing of the 
crank-shaft close to the crank has to withstand all push and 
pull due to the steam effort for which it is the fulcrum, and 
also the weight of the shaft, fly-wheel and attachments, and 
the pull of the belt, if one is used to take the power off from 
the shaft. Furthermore, the shaft turning in this bearing 
must remain very carefully in line both back and forth, and 
up and down. 

To meet these requirements the main bearing must have 
a generous area of contact so that alternate pressure shall be 
unable to become so great as to squeeze out the lubricant 
from the contact-surfaces, and it must be capable of minute 
adjustment to compensate for wear. Fig. 288 shows a usual 
construction of such main bearing, in which, instead of 
two half-boxes as in the stub ends, the bearing-surface is 
made up of four segments. These segmental bearings are 
called quarter-boxes, and in the design shown are separately 



33^ MECHANICAL ENGINEERING OF POV/ER PLANTS. 




CRA NK-SHA FT. E CCEN TRIG. FL V- WHEEL. 



339 



adjustable by means of wedges which come down through the 
massive cap of the bearing. The 
quarter-boxes are the ones which 
have to withstand the steam- 
effort in a horizontal engine, 
while the lower one has to meet 
only weight. Many different 
modifications of the wedge idea 
are to be met in the various 
bed-plate designs, such as set- 
screws through the face or side 
of the bearing and the like, but 
the same underlying principle is 
present in all. The main bear- 
ing requires special and abundant 
provision for oiling, to which 
reference will be made in proper 
course. The outer bearing or out- 
board bearing of the engine-shaft 
has already been discussed with 
the necessity for its adjustment for 
proper alignment. It has to with- 
stand only the weight of the shaft 
and the pull of the belt. Both 
bearings should have length 
enough to prevent the shaft from 
bending under the strains to which 
it is exposed when the diameter 
of the shaft has been intelligently 
calculated. One or the other 
bearing should have collars to 
prevent undesirable endwise mo- 
tion. These collars, however, 
must not offer any danger from 
a seizing caused by expansion 
due to heat. Such a bearing is 
said to be "collar-bound," and excessive friction is the result. 




340 MECHANICAL ENGINEERING OF POWER PLANTS. 

182. The Eccentric. — It has been previously mentioned 
(par. 82) that most valves are driven from an eccentric on the 
shaft. This eccentric, when not forming a part of the shaft- 
governor, will usually be placed just outside of the main bear- 
ing. It will be fastened to the shaft either by keying or by set- 
screws or by both. In a very few cases it is forged solid on the 
shaft. By reason of the diameter of the eccentric the stub 
construction is not usual or convenient, but the rod fits the 
disk by means of a bearing- surface which is called its strap. 




Fig. 289. 

This strap is made in tw^o halves which meet on a diameter at 
flanged surfaces by means of which the two halves are bolted 
together. The large area of contact due to the large diameter 
of the pin makes adjustment necessary only at long intervals 
as slow wear occurs, and this is done either by filing away the 
joint of the strap or by removing the liners of thin sheet 
metal, one by one, which were put in there when the joint 
was first fitted. To prevent sidewise motion of the eccentric- 



CRANK-SHAFT. ECCENTRIC, FLY-WHEEL. 



341 



strap, it is made either to fit in a groove in the face of the 
eccentric, or the eccentric fits in a groove in the strap. The 
latter plan has some advantages, since the strap thus forms a 
trough within which the oil will gather and be retained at the 
bottom, whereas in the other arrangement the oil has a ten- 
dency to run off (Figs. 289 and 290). 



01 




i 





Fig. 290. 

183. The Eccentric-rod and Valve-stem. — The compo- 
nents of the crank-motion of the eccentric which are not 
needed to mo /e the valve must be provided for as in the main 
connecting-rod. Hence there will be a joint of some sort 
between the eccentric-strap and the stuflfing-box at which the 
valve-stem enters the valve-chest. In small and short engines 
the weight of the eccentric-rod will be small, so that it will be 
enough to provide a flexible or pin joint at the end of the 
valve-stem without providing a means to guide the latter ex- 
cept that provided by the stufifing-box. In heavier engines 
the end of the valve-stem may either be guided by a slide, or 




342 MECHANICAL ENGINEERING OF POWER PLANTS. 

a rock-shaft must be interposed which will carry the valve-rod 
and from which the valve -stem will be driven. Where this 
rocking-shaft or vibrating lever is introduced it furnishes a 
very convenient means to modify the throw of eccentric and 
valve, and also gives opportunity for hooking and unhooking 
gear (see Figs. 226 and 183). The principal joints of such 
valve-rod and eccentric-rod may either be stub ends, or hard- 
ened steel pins may be used with hardened steel bushings 
which they fit accurately. The rubbing work is so small that 
such well-made work lasts indefinitely. The eccentric-rod is 
usually fastened to the eccentric-strap by screwing it into the 
latter with a jam-nut to prevent its working loose; in larger 
engines it will be a taper fit brought home with a key. In 
very long engines, such as are met with in river-boat practice, 
the eccentric-rod will be an open-work trussed structure of 
flat rods which ends in the single flat or square rod guided by 
the roller-frame by which it is unhooked. The locomotive- 
rods are usually flat, and are bolted sidewise into recesses 
made for them in a tail formed upon the inner eccentric-strap 
(Fig. 188). 

The valve-stem is the name applied to the short rod which 
enters the steam-chest and actuates the valve. It will be 
either attached to the valve by means of a yoke which em- 
braces the latter, or by a screw-joint with the necessary jam- 
nuts. The valve-rod is synonymous with the valve-stem 
except where the Stevens cut-off is used, where the valve-rod 
is the massive rod lifted by the toes, which carries a bracket or 
offset to which the valve-stem proper is attached by means 
of jam-nuts, whereby careful adjustment is made possible. 

184. The Fly-wheel. — In early engines turning with a 
low number of revolutions, the fly-wheel required to be of 
large diameter, and was for this reason nearly always distinct 
from the wheel from which the power was taken off. In more 
modern engines the convenience of having the fly-wheel serve 
also as an element of the transmissive machinery has brought 
around the use of fly-band-wheels, where belts or ropes are 
used to take o^ the power from the engine-shaft. It is so 



CRANK-SHAFT, ECCENTRIC. FLY-WHEEL. 343 

much less the practice in recent years to use gearing in trans- 
mitting from the engine-shaft that the fly-wheel is very rarely 
a toothed wheel. 

The function of the fly-wheel is threefold. First, to store 
up excess of energy received from the piston in one part of 
the stroke, and to give it out when the effort shall have grown 
less by expansion. Second, to equalize variation in the 
leverage with which the varying steam-effort acts upon the 
crank to revolve the shaft. Third, to give out or absorb 
energy when variation in the external load or resistance occurs 
suddenly. The fly-wheel is therefore an accumulator and an 
equalizer, and the reserve which it stores will be greater as its 
mass is greater and the leverage greater with which that mass 
acts. Since large mass means great weight, it is often con- 
venient to increase the virtual radius of the wheel (mathe- 
matically its radius of gyration), and thus diminish weight 
which causes friction in the bearings. The objection to the 
large wheel is the space which it occupies vertically, and the 
complication in foundation which it causes. With large diam- 
eters centrifugal force in the rim becomes considerable, and 
may become equal to or surpass the tensile resistance of the 
material of the rim. For these reasons it will be found that 
smaller diameters prevail in modern engines, and that roughly^ 
the relation of four times the stroke of the engine is likely to 
approximate the diameter chosen. In early engines thirty- 
foot fly-wheels were often to be met, but now eighteen to 
twenty feet is a large diameter, and in centre-crank high- 
speed engines six feet has become a large size. 

The function of the fly-wheel as a regulator is quite dis- 
tinct from that of the governor. The fly-wheel is to com- 
pensate for instantaneous variations, and give out or absorb 
energy, and maintain a constant speed under variations of the 
equality between effort and resistance which are too small to 
reach the governor and cause a variation of the cylinder-effort. 
For permanent variations, where the load is increased or 
diminished, the capacity of the fly-wheel is soon exhausted, 
and the en^^ine will either increase or diminish its speed. 



344 MECHANICAL ENGINEERING OF POWER PLANTS. 

The governor must then adjust its mechanism to bring the 
engine back to speed, and adjust the piston-effort to the new 
value of the resistance. It is often found in electric-railway 
power plants that wide variations occur in the current upon 
the line without the governor showing any appreciation of 
them. This is to be explained by th'e action of the fly-wheel 
and the absorption and giving out of energy under such 
instantaneous variations. The weight of the fly-wheel must 
be very largely determined by the character of the external 
resistance. A weight capable of equalizing and steadying the 
variations of the cylinder-pressure and of crank-leverage with 
a constant resistance would not be enough to serve as the 
necessary reservoir when heavy demands of power are made for 
short intervals. The best illustration of such wide variation of 
resistance is the rolling-mill engine, in which only the friction 
of the machinery is to be overcome when the train is empty, 
but in which the maximum power of the engine is taxed when 
the piece is between the passes and undergoing the action of 
the rolls. Rolling-mill-engine fly-wheels will have a weight 
of from thirty to fifty tons to meet this requirement, and in 
cable-railway and electric-railway practice, and also with the 
slow speeds of pumping-engines, very massive wheels are 
used. 

185. The Strains in Fly-wheels. — The fly-wheel in rapid 
revolution has its rim in tension by reason of centrifugal force. 
If the ring had no arms, it would be all equally in tension; but 
by reason of the arms resisting extension as the ring expands 
under strain a cross-bending occurs between the arms if the 
wheel is solid, and if made up in segments this bending is con- 
centrated close by the joints. In the second place, as the 
rim is the most massive part and tends to revolve uniformly, 
it will happen that when the resistance slows down the 
engine, the arms will be flexed by the effort of the rim to 
maintain uniform speed, and, on the other hand, the effort of 
the piston when the shaft has lagged behind will tend to bend 
the arms in the opposite direction. Both of these strains 
bring a very serious twisting effort upon the keys by which 



CRANK-SHAFT. ECCENTRIC. FLY-WHEEL. 345 

the wheel is secured to the shaft. If the wheel is a fly-band- 
wheel, the effort of the resistance comes directly to bend the 
arms. In the third place, initial strains of constructiori may 
be present in the wheel, which may superpose their effect 
upon the action of the other two strains. These can be 
greatly increased if the plane of the rim by bad machine-work 
should be out of the plane perpendicular to the shaft. A 
sort of gyroscopic action must occur from the tendency of the 
mass to revolve in the perpendicular plane. The strains from 
shrinkage in cast-iron wheels form a great objection to the use 
oi solid wheels of large diameter of this material. 

i86. Solid and Segmental Fly-wheels. — Small fly-wheels 
can be made all in one piece; the hub (by means of which 
the wheel is fastened to the shaft), the arms, and the rim being 
all cast at the same time. The arms may be straight or curved. 
When straight or curved they are of elliptical or fusiform sec- 
tion, with the long axis in the direction in which the wheel 
turns. The elongated section gives strength against the dis- 
tortion of the rim as speed varies, and moreover opposes the 
least resistance to rapid motion through the air. The straight 
arm is carefully tapered from the hub to the rim, and is 
jointed to both surfaces by wide and generous fillets. The 
objection to the straight arm, and which the curved arm is 
designed to avoid, is the strain of compression in the arms 
and of tension in the rim, which results when the larger mass 
in the rim cooling after the other parts have become solid con- 
tracts in such cooling. The straight arm cannot yield, but the 
curved arm allows a slight bending and relieves the rim from 
strain (Fig. 4). Skilled designers and careful handling in 
the foundry will diminish and almost eliminate these diffi- 
culties, so that the straight arm with carefully proportioned 
masses will be found characteristic of nearly all modern work 
in small sizes and is more workmanlike and pleasing to the 
eye. 

The difficulty connected with the shipment of heavy wheels 
in one piece, and the considerable extent of the contraction in 
cooling in large diameters, results in the practice of making the 



34^ MECHANICAL ENGINEERING OF POWER PLANTS. 

wheels in two halves. This is further a convenience in erect- 
ing the engine. The hub is divided, and each half receives 
an external flange construction so that the hub bolts together 
over the shaft, and the rim is similarly cut and flanged on its 
inside so that each half can be strongly bolted to the other 
(Fig. 1 82). The plane of these joints at hub and rim is usually 
different, so that the bolt-strains may not be entirely axial in 
both sets of bolts at once, and to diminish the difificulty from 
the tendency to fly into two halves by centrifugal force. 

For wheels of still larger diameter and heavier weight a 
segmental construction is usual both for convenience of ship- 
ment, handling, erection, and avoidance of shrinkage-strain 
(Fig. 18). The simple flj^-wheel which does not have to be 
used as a band-wheel, and has a rim .somewhat rectangular 
in section, will have an arm and a segment of the rim cast 
in one piece. The rim-segment will have a length of one- 
half the distance ort each side of the arm necessary to reach 
the adjoining arm on each side, so as to have an appearance 
somewhat like a T with a circular cross-piece. The inner 
end of these arms is inserted in the proper sockets in a 
massive hub, to which they are secured by keys (Fig, 292). 
The rim-segments are joined together by careful fitting 
upon radial planes, and the rim made continuous by a joint 
which appears in several forms. A piece of wrought iron 
may be inserted into a recess in the interior of the rim» 
and taper keys or carefully fitted bolts driven through the rim 
keep this wrought iron a prisoner. A modification of this is 
to have two or four such prisoners let into recesses on the 
sides of the rim if there be but two, and into the inner and 
outer faces also if there be four. Even better than this is the 
use of wrought-iron prisoners which are inserted when red-hot 
into recesses in the rim, so that their contraction on cooling 
shall draw the joint together with a force which is measured 
by their cross-section. These prisoners may be of sections of 
an I, or they may be of the shape of an oval link. The 
recess which they fit enables them to be hammered solid while 
hot, and their projection or hold upon bosses in the recess 



CRANK-SHAFT. ECCENTRIC. FLY-WHEEL. 
8 FT. FLYiWHEEL 



347 




Fig. 291. 



FLY WHEEL FOR BOSTON SEWAGE PUMPING ENGINE. 




Fig. 292. 



34^ MECHANICAL ENGINEERING OF POWER PLANTS, 

forms the joint. Fig. 291 shows a two-part fly-wheel with 
interior prisoner, and Fig. 292 a segmental wheel. 

187. Fly-band-wheels. — When the fly-wheel is to serve 
as a belt-wheel or in rope-driving, the rim requires it to be 
wide rather than deep radially. Such wheels moreover will 
usually be of large diameter, since the linear speed of the 
flexible material used in driving should be high. Such band- 
wheels can be made either by the segmental method shown 
in Fig. 182 or (which is perhaps more usual) the joint between 
the segments will be made at the ends of the arms. The 
arms will be cast solid with the hub and form a spider, and 
each arm will end in a sort of pad, which will form the bear- 
ing-surface for the bolts which unite the ring-segments to the 
arms and to each other. Such band-wheels have no initial 
strains from cooling. 

188. Composite Band-v/heels. — Where great width of 
face is required, more than one set of arms becomes necessary 
to prevent a side flexure from unequal tension at different 
parts of the drum. The unnecessary weight of rim caused 
by the necessity for width if cast iron is used as material for 
the wheel has resulted in the construction of many wheels 
recently in which cast iron is either abandoned or used only 
incidentally. References to these are made in the notes, but 
it may be said that first is the use of wrought iron or steel 
spokes to withstand tension ; next, the use of wood built up in 
segments for the rim with a cast-iron hub and arms; and last 
of all, the use of steel plate. This latter is either used flat or 
dished as a central web, and the rim is built up of the neces- 
sary number of plates, laid edgewise if the wheel requires no 
face, and laid tangentially if a wide face is required. Mass 
and strength has been gotten for the rim by the use of iron or 
steel wire wound around a cast-iron or other rim with suffi- 
cient tension to withstand centrifugal force and supply the 
mass desired. 

189. Conclusion and General.- — Marine engines require 
no fly-wheels, or rather the water-wheel and propeller serve 
this purpose. The locomotive requires no fly-wheel, since the 



CRANK-SHAFT. ECCENTRIC. FLY-WHEEL. 349 

driving-wheels and the Hving force of the engine and train 
serve this purpose. When there are two cranks at 90°, or 
three cranks at 120°, the weight of the fly-wheel diminishes 
rapidly. For rough work in furnaces, rolling-mills, and else- 
where, with quartering cranks a fly-wheel is often dispensed 
with. 

Most fly-wheels of large engines have notches formed in 
their face to make convenient places in which a bar can be 
inserted in order to pry them over the centres if they should 
be caught there. Marine engines have usually special attach- 
ments of screv/ and worm-wheel driven by a small donkey- 
engine for turning them over in port for purposes of inspec- 
tion and repairs. 

Geared fly-wheels revolving faster than the engine-shaft 
have been proposed and used. When driven by belts they 
offer the advantage of compactness, and where the driven 
machinery turns faster than the engine they can apply their 
regulating effect more directly. They have been proposed as 
means of storing energy in central stations and upon railways 
with very steep gradients. The difficulties are those due to 
their friction even with roller-bearings, and the relatively small 
amount of energy which they will store. 



CHAPTER XVIII. 
PIPING FOR THE ENGINE AND ITS ATTACHMENTS. 

190. General. Throttle-valve. — In the previous chapters 
the construction or erection of the engine has been discussed 
up to the point at which the energy resident in steam at high 
pressure is to be conveyed to the engine in order to run it. 
The waste or exhaust steam must be conveyed away from the 
engine, and the water which results from condensation must 
be disposed of or provided for. This gives rise to a division 
of the power plant of some importance and to which careful 
attention should be paid. 

In most cases the throttle-valve is furnished by the builders 
of the engine with the necessary finished flange to bolt it to 
the steam-chest. The erector of the engine must connect 
this throttle-valve by suitable piping to the boiler, connect 
the exhaust to the condenser or the open air, and connect 
drips either to the condenser, to the hot-well, or to outfall 
drainage, as the individual conditions may indicate. With 
respect to the throttle-valve it may be said that its primary 
requisite is to offer least resistance to the passage of steam 
when open, and to close absolutely tight against the passage 
of steam when shut. In small engines it is usually a globe 
valve closing by a screw on its spindle and turned by a wheel. 
In large sizes it will be of the gate-valve pattern opened and 
closed similarly by a hand-wheel, or will be a balanced 
valve operated by a lever. The objection to the gate- 
valve is the difficulty in keeping it tight and in regrinding 
it after it has worn. This difficulty is much mitigated in some 
of the newer forms. It is convenient with the globe valve to 
have it stand with the under side of the valve towards the 
boiler. By this arrangement when the valve is shut there is 

350 



PIPING FOR THE ENGINE AND ITS ATTACHMENTS. 351 

no pressure on the stuffing-box of the spindle, which lessens 
the danger from leakage and makes it easier to repack it when 
necessary. The convenience of this feature overbalances the 
disadvantage of having pressure tend to lift the valve rather 
than to hold it to its seat. Valves with removable faces are 
quite a little used, so that new contact-surfaces may replace 
those which are worn by use and abrasion. The passage of 
steam at high velocity carrying drops of water wnll erode 
metallic surfaces with surprising rapidity. The throttle-valve 
of river-boat engines is usually a pivoted disk-valve. The 
disk of elliptical shape is mounted on an axis coinciding with 
its short diameter, which comes out through the side of the 
cylinder which forms the casing. The edge of the elliptical 
valve is bevelled so as to fit the cylindrical casing and form a 
steam-tight joint at the edges. Such a valve will be in equi- 
librium of pressure on both sides of the axis, and is conse- 
quently balanced. When wide open it stands in the plane of 
the axis of the pipe and practically offers no resistance to the 
passage of steam. The difficulty from the tendency to flex 
restricts its use to comparatively low pressures. The locomo- 
tive throttle is usually a balanced poppet-valve with two 
seats. This arrangement is a necessity with the high pres- 
sures used in this class of engine and where quick operation 
of the valve is demanded. 

191. Steam-pipe. — The diameter of the steam-pipe is 
determined usually by the builder of the engine by the size 
of the throttle-valve which he furnishes. The area of its cross- 
section should be large enough to prevent loss of pressure 
caused by friction of the steam in the pipe, and experience 
shows that this is secured when the linear velocity of the steam 
in the pipe does not exceed 100 feet per second or 6000 
feet per minute. The loss by friction in ordinary lengths at 
this velocity is inappreciable, and if the pipe is short and 
straight, and there are good reasons to justify the practice, 
the engine will work satisfactorily with high-pressure steam 
having a velocity of 8000 feet per minute. Knowing the 
volume- of steam which the cylinder requires per minute, the 



352 MECHANICAL ENGINEERING OF POWER PLANTS. 

cross-section of pipe is easily found or checked. It is desira- 
ble to use no larger pipe than is necessary, on account, first, 
of the cost of pipe and fittings, second the weight, and third 
the increased loss from radiation from the unnecessarily large 
surface. 

Usual diameters of pipe will be of the ordinary standard 
lap-welded wrought iron. Large diameters above that which 
can ordinarily be commanded will be of steel — lap- or butt- 
riveted. Cast iron, which has been much used in the past, 
is little thought of for high-pressure work by reason of its 
weight when strength is required, and its unreliability under 
the strains of unequal temperature and cross-bending with 
expansion. Cast iron is still used to some extent for fittings 
(elbows, tees, and the like), but even for these, steel castings 
give so much better and stronger results as to be preferred. 
When special fittings are made for bends or branches they 
should be made with long easy sweeps rather than the close 
bend usual in standard fittings. Some excellent results have 
been gotten from wrought-iron and steel bends welded or 
riveted. Where wrought-iron pipe of large diameter is 
required the lengths cannot be joined with the ordinary 
coupling, but must be flange-joints. These flanges will be 
steel castings into which the pipe will be expanded rather 
than screwed and the successive lengths will be joined by 
bolting the flanges together with a gasket between. For low 
pressures rubber asbestos-board and combinations involving 
graphite will serve, but with the higher pressures the gasket 
should be metallic. The softer or fibrous joints are easier to 
make, but they blow out when they have become hard by 
heat, and cause leakage and annoyance. The metallic gaskets 
are flat rings of corrugated copper, or of some soft metal or 
alloy, which will be squeezed by the bolt-pressure into 
intimate contact with the flange-surfaces. With faced flanges 
excellent results are secured by cutting rings in the face, into 
which the material of the gasket is pressed. 

In marine practice where deck-beams and general contrac- 
tion of space introduce many corners, and great flexibility 



PIPING FOR THE ENGINE AND IIS ATTACHMENTS. 353 

must be provided, copper steam-pipe is much used. This is 
either made by taking sheet copper, bending it into a cylinder 
and brazing the joint, using brass as a solder, or the pipe is 
drawn or is made without a seam by an electrolytic process. 
The copper in this latter plan is deposited upon a former in 
the desired shape by a successive deposition until the re- 
quired thickness is built up. The pipe is then hammered to 
insure thorough ductility and homogeneity, and the necessary 
flanges are brazed on. Copper lacks the tensile strength of 
steel, so that greater thickness is required; but it has recently 
been proposed to incorporate a winding of steel wire into 
such pipe to give strength while retaining flexibility and 
ductility. Copper pipe expands and contracts without injury 
to itself, and resists corrosion better than iron or steel. 

In large steam-plants where numerous boilers supply many 
engines through a common steam-pipe, the steam-pipe becomes 
the most vital part of the plant. Boilers can be shut off for 
repair and duplicate engines are at hand in case of accident; 
but if the pipe needs to be repaired, the steam must be shut 
from it, and the whole plant must stop. For these reasons 
some of the largest power plants have the pipe also in dupli- 
cate, so that any boiler may furnish its steam to either pipe,, 
and any engine get steam from either pipe. 

The steam-piping for compound or multiple-expansion 
engines usually includes a by-pass connection with a control- 
ling valve leading from the main steam-pipe either before or 
after the principal throttle-valve — usually before — to the 
second cylinder in the series. The object of this by-pass is 
to enable the engine-runner to get steam past the first cylin- 
der in case the latter should be stopped with the distributing 
valve covering the ports so that no steam can enter the high- 
pressure cylinder, or because it is stopped on the centre. In 
cross-compound or triple engines, if the first cylinder is on 
the centre the second is sure not to be, so that by turning 
steam directly into that latter cylinder the engine is started 
and the first cylinder put in position to receive steam in 



354 MECHANICAL ENGINEERING OF POWER PLANTS. 

proper succession. In the compound locomotive with two 
cylinders the intercepting-valve does this automatically. 

192. Expansion of Steam-pipe. Expansion-joints and 
Hanging. — The steam-pipe is connected cold or at the tem- 
perature oi the atmosphere. In service it is heated to the 
temperature of the high-pressure steam passing through it, 
probably in excess of 300"^ Fahr. The coef^cient of expan- 
sion in wrought iron seems to be about .000006 of its length 
for one degree Fahr., according to recent investigations, so 
that for 300° and several hundred feet of length the expansion 




Fig. 300. 

will be a considerable quantity. Different methods may be 
used to provide for this expansion. The first is to arrange 
the pipe so that wherever there is a change of direction there 
is also a change of plane. This is particularly convenient in 
comparatively short lengths, and the change of length is taken 
up in torsion and bending and not in a severe cross-strain 
upon fittings. Where this is not convenient and the straight 
lengths are too great, what are called expansion-joints are in- 
serted. These are of two types. The first is called the slip- 
joint, shown in the upper part of Fig. 300, in which one end 
of the length carries a stuffing-box with gland, and the other 
end a brass sleeve which slides steam-tight in and out of the 
stuffing-box as the pipe expands or contracts. These slip- 



PIPING FOR THE ENGINE AND ITS ATTACHMENTS. 355 



joints are troublesome from leakage when the packing dete- 
riorates, and from a tendency to seize and become hard and 
fast from corrosion and defective alignment of the pipe. 
Care must be taken also that the pipe is not allowed freedom 
of movement sufficient to blow the slip-tube out of the 
stuffing-box from end pressure of steam within the pipe. 

The second form of expansion-joint has copper bends to 
replace the usual elbows. The copper, by reason of its duc- 
tility, withstands considerable deformation. Corrugated brass 
or copper sections permit considerable changes of length on 
each side of them (Fig. 300). 

The third form is used for high pressures and temperatures 
and consists in making a flexible flange-joint of steel plate or 
of copper of wide diameter. The pipe is expanded into the 
middle of this flange and the two edges are bolted or riveted 
together ringwise. The flange opens and closes like a bellows 



] [ 

] [ 
] 



^\^^v^^<m.^^.^^'^^ ^-^^^v.^\^^\^^^ 



Fig. 301. 
under changes of length (Fig. 301). This same type of expan- 
sion-joint is used in river-boat engines to connect the side pipes 
to the upper steam-chest, which is a part of the cylinder-casting. 
The changes of length in the steam-pipe require that in 
hanging it provision be made for considerable motion length- 
wise. The simplest method is to suspend the pipe by rods 
long enough to allow them to swing as the pipe moves. If 



35^ MECHANICAL ENGINEERING OF POWER PLANTS. 

this is inconvenient, a species of roller-bearing may be used^ 
such as shown in Fig. 302. The hanging must not permit 
the pipe to be cramped in its tendency to move. 




Fig. 302. 
193. Grading of Steam-pipe. — Experience shows that 
when steam is moving in a pipe at high velocity it is impossi- 
ble for water of condensation to move against it. It will even 
be carried along in a vertical pipe. Hence the steam-pipe 
should be graded downwards towards the engine from the 
boiler, and provision must be made near the engine to catch 
or dispose of this water. Trouble is often made in pipe 
systems using the ordinary fittings where outlets are made in 
the plane of the axis of the fitting, by reason of accumula- 
tions of water below the level of such outlets. Such pockets 



PIPING FOR THE ENGINE AND ITS ATTACHMENTS. 357 

are the occasion of noise from the phenomenon of concussive 
ebulHtion under certain conditions of heat and pressure; but 
worse than this, the water is sometimes hfted bodily out of 
the pocket with the steam-velocity, and considerable masses 
of it fetch up against an abutting surface upon which they 
strike a smashing blow which it may not be able to withstand. 
Such pockets should either be carefully drained, or, better 
still, a special, form of fitting should be used, such as shown 
in Fig. 303 in which the condensation will flow out of the main 




Fig. 303. 

pipe with the steam which flows through the branch. A few 
pounds of water moving several hundred feet with a velocity 
of nearly a mile a minute, represents a mighty store of energy 
and is capable of most disastrous results. The presence of 
water in such pockets is also the occasion of mechanical 
erosion of the pipe similar to the action of the sand-blast, and 
ample provision must be made to get rid of even small accu- 
mulations. 

194. Drainage of Steam-pipe. — To get rid of accumula- 
tions of water drawn mechanically or entrained by the steam 
from the boiler and those which result from condensation a 
number of different methods may be used. 

The first is to tap into the pipe, wherever pockets and 
elbow-joints occur, small pipes with the necessary valves which 
can be left partly open and draw off water as fast as it gathers. 
These pipes may all converge towards a closed reservoir or 
tank from which the accumulated water may be pumped 



358 MECHANICAL ENGINEERING OF POWER PLANTS. 

back into the boiler. These drip-pipes will vary in size with 
the quantity of water to be taken care of, but nothing is 
gained from having them too small, since they are likely to 
become clogged and inoperative. From one-half inch to one 
and one-quarter will be the usual range, according to the size 
of the pipe and engine. 

The second method is to diminish the losses of heat from 
the flowing of live steam through such tubes by the use of a 
steam-trap. A steam-trap is a pot within which is a device 
which is usually intended to act upon a valve or opening 




RENEWABLE 
VALVE 



Fig. 304. 

when water is to pass through it, but to refuse to act wheit 
water changes to steam. This result is secured in many- 
ways in different designs of trap. The simplest plan is to 
have the trap inclose a float which is acted upon by water 
and raised, but which falls in steam. It will be seen that 
when the drip-pipe connected to the trap is filled with water, 
the float will lift and open the connection through which that 
water can escape. When trap and pipe are emptied of water 
the float will fall, closing the outlet from the trap, and shut- 
ting off escape until the trap is again filled. The discharge 
from these traps may either be back into a closed tank to be 
pumped into the boiler, or it may be wasted into drains (which 
is not to be commended). Many traps instead of using a 
float are operated by differences of expansion of one or two 
metals in steam and water. 



PIPING FOR THE ENGINE AND ITS ATTACHMENTS. 359^ 



The third method is to introduce a receiver or catch- 
water tank in the pipe close to the engine into which all con- 
densation shall be made to flow, and out from which only dry 
steam will go to the engine. Such a receiver may be a pipe 
(Fig. 305), or a simple vertical cylinder of boiler-plate, into the 




onm cocK^ 




Fig. 305. 



top of which the steam-pipe enters and passes down part way. 
The water which is carried by the steam falls to the bottom 
by its inertia or by gravity, and will there be taken care of 
either by a drip-pipe or by a trap. The steam going to the 
engine leaves the receiver from a point near the top, and the 
enlarged diameter which diminishes the linear velocity of the 
steam prevents the outflowing current from drawing out the 
entrapped water. A glass tube can be attached to the side 
of the receiver so that the level of the water caught in it can 
be easily observed and its discharge governed accordingly 
(Fig. 306). 

The fourth method is easily derived from the foregoing. 



360 MECHANICAL ENGINEERING OF POWER PLANTS. 



It is the use of a separator to withdraw by mechanical means 
water which the steam has entrained. There are several 

forms of such separators. One of 
the most successful ones is shown in 
the right-hand part of Fig. 305, and 
its method of application is obvious. 
It will be seen that the principle in- 
volved is that of giving a spiral or 
centrifugal motion to the water and 
steam as they enter the separator. 
The superior density or weight per 
cubic inch of the water causes it to 
yield most strongly to this centrifugal 
tendency, and it goes to the outside 
of this chamber, while the lighter 
steam being less affected by this 
tendency, will remain nearer the 
centre, from which the outlet to the 
engine is taken off. The presence 
of metallic-surface perforated deflect- 
ing- or baffle-plates and similar con- 
structions increases the efficacy of 
the separator, since water divided in 
drops has a tendency to attach itself 
by capillary action to such surfaces. 
The separator requires to be, in the form shown, of a diam- 
eter at least twice that of the pipe, and the depth or length 
at least three or four times its diameter. The larger the 
separator the more efficient, since it combines in this case 
the natural separation by differences of specific gravity with 
the mechanical separation by centrifugal action. The sep- 
arator acts as a receiver when accidental quantities of water 
are thrown over with the steam. With reasonably dry steam 
(having five per cent of water in it or less) an effectual sep- 
arator should allow less than one per cent of water to pass 
it and reach the engine. The discharge from the bottom of 
the separator may be taken care of by a trap, or it may be 
freed by hand as above described. Fig. 307 shows a cen- 




PIPING FOR THE ENGINE AND ITS AT TACHMENTS. 36 1 

trifugal separator for a horizontal line of pipe. The heavier 
water is thrown radially and caught in the receiver below. 
An exceedingly clever substitute for the trap has been 




Fig. 307. 
recently worked out for this purpose in places to which it 
can be satisfactorily applied. It is called the steam-loop 
and is shown in Fig. 308. The pipe from the bottom of 




Fig. 308. 
the separator becomes a species of siphon, whose length of 
leg is depended upon to move the water in it by the dif- 
ferences of density of the water in the two legs. In the 



362 MECHANICAL ENGINEERING OF POWER PLANTS 

drop-leg of the loop, which is connected to the boiler belowr 
the water-line, the water is comparatively still and solid. In 
the other leg or riser the water is mixed with steam in bubbles 
ascending up through it, and this difference in weight will 
maintain a continual discharge into the horizontal member, 
which is slightly graded towards the boiler. The steam- 
pressure is nearly in equilibrium at the level of the water-line 
through the system, but the weight of solid water in the drop- 
leg gives the dynamic head to feed the condensed water con- 
tinuously from the drop-leg into the boiler. 

195. Non-conducting Coverings. — If the surface of the 
steam-pipe were left bare with hot steam within it, the currents 
of air circulating around the pipe would convey off a great 
deal of heat by contact, and the pipe furthermore would 
radiate heat to surrounding objects. Both of these would 
cause condensation of steam and loss of pressure, and would 
add to the discomfort of those who are compelled to work in 
the engine-room. It is therefore universal to cover the sur- 
face of the steam-pipe with some material which shall keep 
air-currents from the pipe and shall resist by its properties the 
tendency of the pipe to radiate. These two requirements 
must be kept in view in selecting the material to be used. 
The material must furthermore be resistant to combustion 
and deterioration under heat, and must give off no disagree- 
able odors. It must be easily applied, must be cleanly and 
not attractive to vermin, and it is desirable that it be so made 
that repairs and alterations to the pipe may be made without 
destroying the non-conductive covering and making its renewal 
necessary. These latter conditions point to the use of what 
are called sectional coverings. 

Since air undergoes no heating by radiation, bu't is heated 
by contact only, it has been found that materials of such 
porous or fibrous character as to shut in or occlude a consid- 
erable quantity of air, finely subdivided, make the best non- 
radiating coverings. The air is easily heated ^by contact, so 
that care must be taken to prevent this air from circulating, 
^nd it is best to keep it from actually touching the pipe. 
These peculiarities form the basis for the excellence of many 



PIPING FOR THE ENGINE AND ITS ATTACHMENTS. 363 

combinations which use hair-felt. The porous or fibrous 
quahty of the hair-felt holds a large quantity of air while cir- 
culation is precluded, and injury to the hair is prevented by 
first wrapping the pipe with asbestos- board. The hair is held 
in place by a canvas covering sewed over it, and if desirable 
bound by sheet brass or nickel-plated rings for appearance' 
sake. The fibre of asbestos or of blast-furnace cinders com- 
minuted by blowing air or steam through it while fluid, and 
known as mineral wool, possesses the same qualities as hair- 
felt, and for the same reasons. Other materials of successful 
use as non-conductors belong to the class of the earths. 
Infusorial earth largely composed of the silicious shells of 
minute diatoms, magnesian earth, ashes, and the like, made 
into a plaster with some binding material like asbestos-fibre 
or hair, form a group of non-conducting coverings often to be 
met with and which form the plastic class. The sectional 
coverings or removable coverings are combinations of asbestos- 
paper, hair, and canvas moulded into split cylinders which are 
sprung on over the pipe, closed together,and held by decora- 
tive bands. References to the ef^ciency of these and other 
non-conducting coverings will be found in the notes. It is 
apparent that to increase the thickness of the coverings in 
order to diminish loss of heat through them is to increase the 
cost of such coverings and the weight of the pipe. The pres- 
ence of the covering compels the hanging appliances to adjust 
themselves for expansion without disturbing the covering. 

196. Exhaust-pipe. — In non-condensing engines the ex- 
haust-steam should escape from the cylinder with the least 
possible resistance from friction or bends in the pipe which 
conveys it away. Such resistance is continually a subtraction 
from the effective power of the working stroke. For this 
reason it is usual to make the exhaust-pipe for a given engine 
a little larger than the steam-pipe in the proportion that the 
velocity of flow in it should be about two thirds that in the 
steam-pipe, or at a rate not exceeding four thousand feet to 
the minute. In small engines this is readily secured by hav- 
ing the exhaust-pipe one size larger than the steam-pipe. In 
condensing engines the exhaust-pipe will be short and usually 



3^4 MECHANICAL ENGINEERING OF POWER PLANTS. 



direct, and where this is the case the vacuum will be estab- 
lished in the exhaust-pipe as well as in the condenser. 
In non-condensing engines the pressure in the exhaust-pipe 
will be that of the atmosphere, or at most a pressure rang- 
ing from that up to three pounds per 
square inch. Hence it need not be of 
the same strength as the steam-pipe, 
which explains the use of spiral riveted 
or spiral welded pipe in long lengths 
(Fig. 309). Lightness and cheapness 
are thus secured. In city conditions 
the exhaust-steam must be taken to 
the roof of buildings or factories to be 
discharged, which compels a consider- 
able ascending length of pipe. In 
power plants where this does not have 
to be considered the engine may ex- 
haust into the open air at its own level. 
Where the noise of the exhaust is of 
no consequence as it escapes into the 
air, the end of the pipe may be bare. 
Where noise must be prevented, and 
where the discharge of condensed 
water in the exhaust current carrying 
oil from the cylinder is objectionable 
or harmful to roofs or structures, pro- 
vision must be made to meet both of 
the'se difficulties. This is done by 
what is called an exhaust-head. Fig. 
3 10 shows typical arrangements of such 
an appliance. It is like a separator in 
principle. The water and oil striking 
the deflecting surfaces are caught by 
them and drop downwards, and are car- 
ried away by the drip-pipe, while the steam is discharged 
over the largre area of the base of the inverted cone with so 
reduced a velocity that its escape is noiseless. Similar re- 
duction of velocity is also to be secured by baffling th.e dis- 




FiG. 309. 



PIPING FOR THE ENGINE AND ITS ATTACHMENTS. 3^5 



charge by perforated diaphragms, wire netting, layers of balls, 
and the like. 



HOBERTSOIV 




ECLII>SE 
Fig. 310. 

197. Oil-extractors. — In non -condensing engines with an 
exhaust-head oil descends through the drip-pipe with the con- 
densation, and can either be caught, if valuable, or discharged 
to waste, if valueless. In condensing engines the lubricant 
used in cylinders and valve-chests will pass to the condenser 
and hot-well with the steam. Part of it will be caught in the 
surface-condenser, which it will' foul and in which it will give 
trouble, and that which goes to the hot-well will be pumped 
from that well into the boiler, w4iere again it will cause great 
annoyance. It does not pass out with the steam, but remains 
behind accumulating in quantity as the interval between 
cleanings of the boiler is larger. It will be seen in due course 
(par. 339) that its presence is a continual danger causing local 
or general overheating, making the plate corrode and an in- 



Z^^ MECHANICAL ENGINEERING OF POWER PLANTS. 



ternal boiler-furnace to become deformed. It is in every way 
desirable to extract the oil from the exhaust before it enters 
the condensing appliances. This is done in many ways by 
what are called oil-filters or oil separators. Their principle 
is to catch the oil upon the extended surface of some 
material through which the steam will pass but the oil will 
not. Hay or straw, compressed sponge, or sand in a tight 



STEAM FROM BOILER 




Fig. 311. 

box represent types of such oil-filters which are cheap but 
troublesome from the necessity for frequent renewal of the 
filtering material. Fig. 311, showing the Edmiston oil-filter, 
presents a type of apparatus using cloth as the filtering 
medium. The advantage which this type offers is the com- 
parative ease with which frequent renewals of the filter can 
be made. Figs. 312 and 313 show forms of separators 
designed to separate oil from steam by catching it upon 



FIFING FOR THE ENGINE AND ITS ATTACHMENTS. 3&7 

metallic surfaces to which it shall be held by capillary action 
until enough accumulates to drip off into catch-pockets. 




Fig. 313. 
They work with cold or wet steam, but not with hot or high- 
pressure steam, which seems to divide the oil so finely that it 



368 MECHANICAL ENGINEERING OF POWER PLANTS. 

runs through such separators without catching upon their 
surfaces. 

Chemical means using alum for coagulating and eliminat- 
ing the oil are open to the objection that they need continual 
care and superintendence to secure ef^cient working. 

198. Drip-connections. — In non-condensing engines with 
the valve-chest on the top of the cylinder, the outlets from 
the cylinder-cocks require to be piped to the waste- or 
drainage-outlets. Such connections will carry through them 
more or less oil, so that they should not be too small. The 
steam-pipe which descends to the engine from an upper level 
should have a pocket close to the throttle- valve at the bottom, 
from which a drip should be connected so that the steam-pipe 
can be thoroughly heated and freed from water before the 
throttle-valve is opened. This can be a smaller connection, 
since only distilled water is to pass through it. The third 
drip-connection will be from the lowest point of the exhaust- 
pipe either where it leaves the engine, or at the elbow where 
it starts to rise towards its roof-outlet, or at both points. 
This drip will have to take care of some oil, and consequently 
should be large enough to be in no danger of clogging. 
These several drips should each be controlled by its own 
valve, usually a globe valve, which can be easily operated by 
its hand-wheel when hot. Drips from the cylinder may be 
dispensed with in engines having the valve-chest on the 
bottom or at the bottom of one side, if the distribution by 
the slide-valve is such that the exhaust-port can be used as a 
drip-connection clear to the end of the stroke. Many engines 
have the distibuting valve capable of lifting from its seat by 
pressure underneath it so that an excess of water may find 
vent in this way. With positive pressure-plate valves this 
cannot usually be done (see pars. 103, 104). Where drainage 
from the cylinder goes out at the exhaust, special care must 
be taken to have the exhaust-drip generous and effective. In 
condensing engines the same drainage or drip-connections for 
the steam-pipe must be provided, but in most cases no cyl- 
inder-drips are needed, since condensed water will pass out to 
cne exhaust by vaporization, and by gravity in cases where 



PIPING FOR THE ENGINE AND ITS ATTACHMENTS, 369 

the condenser is below the cylinder, as is usual. With gravity- 
condensers drips must be used, but must be operated with 
care, because after the vacuum is created they will work back- 
ward and mar the vacuum. In condensing engines the drips 
can profitably be connected to the hot-well, so that the warm 
water which they discharge will be pumped back to the boiler 
instead of being wasted. 

In compound or multiple-expansion engines, besides the 
drip from the steam-pipes and the high-pressure cylinder going 
to the hot-well, there will need to be provision for draining the 
receiver between the cylinders. There should not be fluctua- 
tion of pressure sufficient to vaporize hot water entrained or 
condensed in the receiver, nor is it advisable to allow such va- 
porization to take place. Hence the receiver of such engine 
will be piped from its lowest point to the hot-well and with a 
trap in its connection. In jacketed engines the water of con- 
densation accumulated in the jacket must be drained off by 
proper pipes. Where it is possible to do so the jacket-drains 
should return their condensation to the boiler by traps direct 
rather than to suffer the loss of heat caused by the drop of 
pressure in passing into the hot-well. This is a measure which 
tends as well to making the engine efficient. A recent success- 
ful design of triple engine has the steam for the independent 
air-pump taken from the drip connections of the jackets. Cir- 
culation is maintained through the jackets, and no waste occurs. 

199. Sundry Connections and Attachments. — The piping 
necessary for the proper working of an exhaust-steam feed- 
water heater, the piping for the lubricating appliances, the 
heater itself, and the lubricators will receive discussion under 
the subdivision in a later chapter in which they properly fall. 
The same is true also of the gauges and apparatus of their 
class which form a part of the engine-room equipment. 

200. Summary. — It has been the desire and intention to 
review the construction and appliances which are to be ex- 
pected in a power plant so far as relates to the modern engine 
in the foregoing chapters which have covered the engine sub- 
division. In the succeeding chapters the boiler and furnace, 
the setting, and accessories are to be similarly considered. 



CHAPTER XIX. 
THE STEAM-BOILER. GENERAL CONSTRUCTION. 

201. Introductory. — By reference to pars. 2 and 5 it will 
be seen that the energy resident in a fuel or source of heat 
has to be liberated by combustion in a furnace, and that this 
energy thus liberated is to be stored in a suitable vessel or 
reservoir from which it may be drawn off as required. The 
foregoing chapters have treated of the energy communicated 
to' the engine through a steam-pipe, and the next series of 
chapters is to treat of the generation of pressure and its stor- 
age in the vessel which is called the boiler. Two points of 
view are therefore of prime importance in viewing the steam- 
boiler. The first is economy in the liberation of energy from 
the fuel and the generation of pressure in the boiler. The 
second is safety in the storage of that heat-energy. Economy 
may be expected from three points of view., First, economy 
in first cost of the boiler and its appurtenances and in the 
setting which it may require. Second, economy in the com- 
bustion of the fuel or in the number of foot-pounds of energy 
derived from the heat-units resident in the fuel. Third, 
economy in maintenance and repairs, in which would be 
included depreciation from use and age. The safety in stor- 
age is mainly against rupture, whereby injury is done either 
to person or property from hot water or steam escaping in 
quantities, or by the sudden release of the stored energy all 
at once producing the disaster which is called a boiler- 
explosion. 

202. Shapes for Steam-boilers — Since the steam-boiler is 
to withstand pressure from within, equal in every direction, 
the shape which is at once suggested for such a reservoir of 
pressure is the sphere. The fluid pressure being normal to 



THE STEAM-BOILER. GENERAL CONSTRUCTION. 371 

the enveloping surface is decomposed equally in every direc- 
tion when that envelope is a sphere, so that there is no ten- 
dency for a spherical boiler to change its shape or undergo 
flexure. The normal strains are opposed by the tensile 
resistance of the material used. Early historic forms of boiler 
present the sphere as a shape underlying what have been 
called the balloon and haystack boilers. The difficulties of 
construction due to the double curvature of the plates 
required in a spherical boiler, and the fact that the sphere is 
not adapted to receive heat which is to be transferred to the 
water from the fire, have been reasons why the sphere is no 
longer used except in aggregations of small spheres in boilers 
of the sectional type. 

The cylinder when strained in a plane perpendicular to its 
axis offers the same advantage as the sphere. Fluid pressure 
from within does not tend to change its shape. The ends of 
the cylinder may be either flat or curved, and if curved they 
may be concave inward or outward. The flat head or end 
tends to bulge by internal pressure, and will keep on bulging, 
if the material will allow, until the end surface has become 
hemispherical. When this happens the spherical decomposi- 
tion of the forces is restored and no further deformation takes 
place. If the head is concave outward, it receives internal 
pressure like a dome ; and if deformation is prevented, it resists 
like the hemispherical-ended boiler with the material of the 
head in compression instead of in tension. The hemispherical- 
ended boiler has been somewhat used and is called the ''egg- 
ended " boiler. The sheets which make the head are trouble- 
some to form, however, and it is little used in America. 
The flat head is almost universal, and is practically a necessity 
where flues or tubes are to be attached to it. Such flat heads 
require to be stayed or braced to prevent bulging. The 
cylindrical shell and flat-stayed head will be found to be by 
far the most widespread shape. 

203. Materials for Steam-boilers. Copper and Cast 
Iron. — The requisites of a proper material to withstand the 
elastic tension of the steam-gas are sufficient tensile strength 



372 MECHANICAL E'NGINEERING OF POWER PLANTS. 

and a ductility to enable it to withstand such strain without 
breaking. In addition to the stretch caused by internal 
pressure the material forming the envelope of the gas must 
resist the strains caused by heat. These strains are not only 
those caused by expansion, but more trying than these are 
the strains due to sudden contraction in the structure when 
cold water is introduced to supply the steam withdrawn, and 
when cold air impinges upon a hot surface from the opening 
of a furnace-door or through defects in the setting. 

The five materials used about boilers and entering into 
their construction are copper, brass, cast iron, wrought iron, 
and steel. The advantages of copper are : 

1. It has a high conductivity for heat, so that the heat of 
the burning fuel is transferred rapidly to the water which is 
to be transformed into steam-gas. 

2. Copper plate is uniform and free from local defects and 
highly ductile. This makes it yield to sudden strains without 
danger of rupture. 

3. This ductility makes copper plate easily shaped. The 
early boilers made before tools were perfected were largely of 
copper for this reason. 

4. Copper resists the corrosive tendency from the gases in 
the fuel and from certain kinds of water. 

5. Scale due to precipitated mineral matter in the water 
does not adhere to copper as firmly as to iron. 

The objections to copper as a material for boilers are: 

1. It has a tensile strength of only 32,000 to 33,000 pounds 
per square inch, while wrought iron has over 40,000 and boiler- 
steel has about 60,000. This makes copper boilers thick if 
they are to be strong; their thickness makes t?iem heavy, and 
their weight makes them expensive. Modern boilers use 
copper plate only in the fire-boxes of locomotive boilers, 
where they can be strongly stayed so as to receive strength 
from the staying. 

2. Copper is too soft to withstand mechanical injury in 
fire-boxes from the firing-tools used by the fireman in handling 
his fire. Where copper is used in tubes, as in fire-engine prac- 



THE STEAM-BOILER. GENERAL CONSTRUCTION. 3/3 

tice and in foreign locomotive practice, the abrasive action 
'from sharp cinders drawn rapidly through the tubes by the 
forced draught wears them rapidly and makes them thin. 

3. Copper loses its strength as the temperature rises. At 
500° Fahr. it loses 2 5 per cent, and at 800° it loses 50 per cent, 
of the strength while cold. 

4. Where copper is used in connection with iron or steel 
shells in waters containing even dilute acids, the combination 
makes a galvanic couple, and the iron or steel, having the low^er 
potential, undergoes corrosion and waste. 

Brass is only used in tubes in boilers where rapid steam- 
ing and transfer of heat are of prime importance. Its advan- 
tages and disadvantages are the same as those of copper. 
Brass mountings about the boiler evaporating acid water will 
often occasion similar galvanic action. 

Cast iron as a material for boilers has the following 
advantages : 

1. It is molded to its shape and poured from a flu-id state. 
Any form can thus be secured. 

2. Within limits it does not require to be joined by rivet- 
ing. 

3. It is cheaper per pound than the other materials. 

4. The corrosive action of the fuel-gases does not waste it 
as rapidly as the other forms of iron. 

The objections to cast iron are: 

1. Its relatively low tensile strength. This will range 
from 12,000 to 20,000 pounds per square inch in ordinary 
grades, although a quality known as gun or car-wheel iron has 
a stength of 30,000 pounds per square inch. 

2. Most of the cast irons are not ductile to any great 
extent, so that when they are strained they break suddenly 
and without previous warning. The sudden release of pres- 
sure by such a break is calculated to permit so rapid a forma- 
tion of steam-gas as to cause the disaster called an explosion 
to follow the rupture. 

3. This absence of ductility makes cast iron ill adapted to 



374 MECHANICAL ENGINEERING OF POWER PLANTS, 

resist sudden differences of temperatures. Sudden contrac- 
tions make cast iron break. 

4. Cast iron is liable to blow-holes which may escape the 
most critical inspection. Their presence inside a casting will 
cause an unsuspected weakness to resist strain. 

For these reasons the use of cast iron is restricted in good 
practice to small parts of what are called sectional boilers and 
to fittings and mountings. Its use is diminishing even for 
these latter purposes. It should never be used where subject 
to rapid changes of temperature. It will be found in heads 
of domes to some extent by reason of the convenience which 
its necessary thickness offers for the attachment of valves and 
fixtures. The best sectional boilers will have little or no cast 
iron in their structure. 

Malleabieized cast iron, commonly called malleable iron, 
is sometimes used in sectional or coil boilers. The removal 
of carbon from the casting in the malleableizing process makes 
it tougher and more ductile than plain cast iron. It is open 
to the objection that the effect of malleableization may not be 
produced clear through the casting, making it unreliable or 
variable in quality. It also has not the same coefficient of 
expansion as wrought iron, which gives trouble when they are 
used together. 

204. Wrought-iron and Steel Boilers. — By far the largest 
proportion of modern boilers, and all of those which have 
a cylindrical shell of large diameter, are made of wrought 
iron or mild steel. The advantages which are offered by 
wrought iron and steel as compared with other materials are 
their higher tensile strength with all necessary toughness, 
elasticity, and ductility. The tensile strength of good boiler- 
plate of wrought iron will be a little over 40,000 pounds to 
the square inch. For steel it is usual to specify that the 
tensile strength shall be not less than 55,000 nor more than 
65,000. The inferior limit secures that steel of pure quality 
shall be furnished, and the superior limit precludes that 
strength being secured by adding excess of carbon, whose 
effect would be to make the steel harder and less ductile. 



THE STEAM-BOILER. GENERAL CONSTRUCTION. 375 

The mprovements in the process for the manufacture of 
plates by the steel-makers have brought it about that wrought- 
iron plates of a quality suitable for boiler-making are more 
expensive than steel plates. This is particularly the case 
with boilers requiring thick sheets. The proportion of black- 
smiths who feel a confidence in their welded work in wrought 
iron rather than in steel induces many designers to prefer that 
braces, stays, and the like should be of wrought iron even 
when the shells are of steel. When iron plates were generally 
to be met, seven grades of wrought iron were recognized. 
The most inferior was called tank-iron, and was rolled from a 
pile made up of muck-bar. It was only rolled once, and had 
more or less cinder in it so that such quality of iron should 
never be exposed to heat. The second grade was called 
refined iron, and was made up of twice-rolled iron. The 
third quality was shell-iron, which might be used in parts of 
the boiler not exposed to the direct action of heat. These 
three grades were made up of any stock, and no specification 
as to quality or process was made. The fourth quality was 
charcoal number one, usually abbreviated to C. No. i, in 
which the purer grade of iron supposed to result when char- 
coal was used for fuel for smelting it in the blast-furnace was 
to be used in the pile. The fifth was charcoal hammered 
number one, abbreviated usually to C- H. No. f, in which not 
only was the charcoal-iron specified, but the ball from the 
puddling-furnace was to be treated for the expulsion of cinder 
under the hammer and not by a squeezer. The best grades 
were flange and fire-box iron, in which not only was selected 
material used, but in piling it for rolling a certain proportion 
of old boiler-plate was to be embodied in the pile and laid 
transversely to the length of the pile. This gave a toughness 
and closeness of texture when rolled twice or more so as to 
enable the plate to be bent at its edges or elsewhere without 
cracking. The repeated rolling and the use of purified stock 
made the plate more thoroughly homogeneous, so as to be 
abl3 to withstand the intense heats of the fire-box or furnace 
in Incomotive or other internally-fired boilers. 



'iJ^ MECHANICAL ENGINEERING OF POWER PLANTS 

The objection to wrought iron as the boiler material is its 
tendency to laminate or blister or both. This tendency is 
caused by the separation of the component layers or leaves of 
which such plate is made up as a result of the piling process 
which wrought iron has to undergo. vv^'hen the layers have 
not been thoroughly welded together, or, worst of all, when a 
layer of cinder unexpelled in working lies between two layers 
of iron, the transfer of heat through the plate is not perfect, 
nor the withdrawal of heat from the iron by the water. The 
consequence is that the outward layers between the fire and 
the defective weld expand more than the inner layers, 
whereby the defect is extended, and presently the outward 
layers bag downwards and separate from the inner layers. 
When this occurs the bagged portion is overheated most of 
the time and oxidizes. The bag or blister is thus a weak spot, 
and in time it becomes perforated or cracks. A blister may 
occur also in steel boilers from a blow-hole, and in any boiler 
as the result of local overheating caused by any grease or dirt. 

205. Steel Boilers. — These special reasons lead to the use 
of steel, but the displacement of wrought iron for boilers is 
a result of other conditions besides the commercial or metal- 
lurgic one referred to above. These advantages are: 

I. The ereater tensile strength with the same ducility 
enables a lighter boiler to be used with the same strength or 
a stronger boiler with equal weight. The use of thinner plate 
diminishes the tendency to overheating at lap-joints, and 
favors a more rapid and effective transfer of heat to the water 
within the shell. Where heat is transferred by contact from 
hot gases passing from a hot fire-box over the metal of the 
shell and thus out at the chimney, it will be apparent that 
time enters as a factor in the process of absorbing heat from 
these causes. If the outward surface of the metal in the 
shell is kept cool by the water within the shell, it will with- 
draw heat from the gas more completely than if the plate is 
thick, whereby a greater difference of temperature has to pre- 
vail between the inner layer of the plate touching the water 
and the outward layer touching the gas. 



THE STEAM-BOILER. GENERAL CONSTRUCTION. 2)77 

2. The greater density of steel enables it to resist abrasion, 
and in some cases corrosion, better than iron. 

3. The fact that steel is made from an ingot cast in a fluid 
state, and the plate is rolled down from this solid ingot, pre- 
vents the presence of welded surfaces which maybe defective 
and cause blisters. This superior homogeneity of steel as 
compared with iron will also explain in part the more rapid 
transfer of heat through steel. 

4. The rolling of steel plates from massive ingots by very 
heavy rolling-mills enables steel plates to be obtained of larger 
size than those rolling iron are capable of furnishing. The 
modern rolling-mills have a distance between housings of nine, 
ten, or eleven feet, which alone limits the width of plate which 
they can roll, while the length in the direction of the rolling 
is limited only by the weights and sizes convenient to handle. 
Sheets eight or nine feet wide and fourteen feet in length are 
easily obtainable, and thicknesses up to one and one-quarter 
inches are quite usual. Steel must be used for these consid- 
erable thicknesses when high pressures and large diameters 
demand them. It would be impossible to work a pile of 
wrought iron having sufficient initial thickness to finish at this 
final thickness and receive work enough in rolling to be of 
satisfactory quality. 

The objections to steel have been its tendency to crack 
from a species of brittleness either at riveted joints or where 
it was bent in order to flange it. The difficulty is not with 
the steel itself, but with its selection or treatment. If steel 
too high in carbon is selected for boilers, it is liable to crack 
by reason of its hardness. Phosphorus in steel as an impurity 
will make steel brittle, but specifications can be drawn as to 
chemical constitution of boiler-steel which will prevent this 
difficulty. Cracking due to improper treatment may be 
prevented by having the steel annealed by heating and very- 
slow cooling after it has undergone shearing, punching, and 
flanging. Annealing removes strains caused by unequal 
heating, and restores the ductility of a good quality of steel 



37^ MECHANICAL ENGINEERING OF POWER PLANTS. 

if the latter has been destroyed from the blows or shocks of 
the shaping processes. 

Some steels have given trouble from a more rapid corrosion 
than the wrought-iron boilers showed which were replaced by 
steel. Usually, however, other conditions were changed with 
the change to steel, and the general experience is that steel 
boilers last longer. 

The steel used for boilers is usually open-hearth steel 
having the properties of iron or ranging less than .50 or one 
half of one per cent of carbon. 

206. Testing of Boiler-plate. — The testing of the plate 
to be used for boilers should be very carefully attended to 
under all circumstances. The federal government have legis- 
lated in this matter with respect to all boilers engaged in the 
interstate trade at sea and in coast waters. They demand 
that every plate used in a boiler shall be stamped with the 
name of the maker, and with the tensile strength determined 
by a test in a proper testing-machine. Such tests are usually 
made upon a strip cut coupon fashion from the end of the 
plate. The shape of test specimens is specified and their 
behavior. Iron with a strength of 45,00c pounds is to show 
15 per cent reduction, and steel 25 per cent of stretch in a 
length of 8 inches. The old demand when steel was first 
introduced was that the contraction of area in drawing down 
at fracture should be 50 per cent in plates one-half inch thick 
or under. Bending tests are also required, as a rule, to pre- 
vent the presence of hardeners such as carbon and phosphorus. 
For thicknesses of three quarters of an inch and under, the 
plate should bend double, both hot or cold, under a heavy 
hammer without showing cracks at the bend, and thicker 
plates should bend with a radius equal to their own thickness 
at the inside without distress. 

207. Thickness of Boiler-plate. — The cylindrical boiler 
exposed to pressure on its inside tends to part along a round- 
about or ring seam by pressure against the heads, and it tends 
to part along a longitudinal seam and open out into a flat 
plate. If the pressure on each square inch be denoted by Py 



THE STEAM-BOILER. GENERAL CONSTRUCTION. 3/9 

and the diameter of the cylinder be D in inches, the area 
exposed to pressure to blow out the head or rupture a ring- 
seam will be the area of the head in square inches multiplied 
by the pressure on each square inch : 

PA = P7tr' = Pn —. 
4 

The resistance to this pressure is offered by a ring of the 
boiler-metal whose area is 

2 7zrt 

when t is the thickness. If / be the tensile strength per 
square inch, the rupturing force just balances the holding 
resistance of the material when 

Pn — = 2 7irtf, 
4 -^ 

This simplifies into 

PD = A,tf. 

For the resistance to rupture along a longitudinal seam it can 
be proved mathematically that the tendency to rupture in any 
plane will be the sum of the components of the normal press- 
ure at every point which are perpendicular to that plane. 
Therefore on each inch in length of such longitudinal seam the 
total pressure is PD. This can also be made clear by the ex- 
pedient of imagining each semi-cylinder of the boiler to be 
nearly filled with a solid material like wood, and that the press- 
ure P is introduced into the narrow space left between the two 
semi-cylinders which are held together by the enveloping ring 
of boiler-plate. The resistance to separation of these semi- 
cylinders is the sum of the areas of boiler-plate at the two 
sides, multiplied by the tensile strength per square inch of 
that plate. This resistance is denoted by 2// when the ring 
has a length of one inch. Hence the equilibrium of bursting 
pressure and resistance along a longitudinal seam is reached 
when 

PD = 2tf. 



380 MECHANICAL ENGINEERING OF POWER PLANTS. 

It will be noticed that the boiler is twice as strong against 
blowing out the head or rupturing a ring seam as it is against 
rupturing along the longitudinal elements of the cylinder. 
This explains why boilers are double-riveted or are made with 
special joints for their longitudinal seams. 

The above calculation is for solid plate, or for welds which 
are as strong as the solid plate. Where riveted seams are 
used an allowance must be made for the reduction of the 
value for f due to the weakening caused by removing the 
metal at the rivet-holes, which the rivets do not replace. 

Boilers are usually designed with a factor of safety of six 
in their shells; or in other words, the working pressure is one 
sixth that at which the shell would be expected to rupture 
from internal pressure. 

Boiler-plate can be bought of all thicknesses, but it is usual 
when the calculation brings out an inconvenient figure to pass 
to that practical thickness which is next above. Usual thick- 
nesses of plate are, in fractions of an inch: 

3 1 5 3 7 1 9 537ttIt1 

T¥' ¥' TF' ¥' T¥> 2"' TI' "S"' T' 8"' *' ^¥' ^¥* 

It is inconvenient to handle, curve, and rivet plate thicker 
than one and one-half inches. The difficulty of manufactur- 
ing thicker plates also stands in the way of their use. A less 
thickness can be made to serve by using a smaller diameter. 

208. Curving of Plates for Shells. — The plate is received 
flat from the manufacturer, and must be bent into the cylin- 
drical shape. This is done by rolling it cold between three 
driven rolls, so arranged that as the plate is moved and driven 
by two of them it shall be continuously pressed by the third 
and caused thereby to receive a continuous curvature. Such 
rolls are called bending-rolls, and may be arranged with their 
three parallel axes horizontal or vertical. The horizontal 
arrangement is much preferred in America by reason of its 
convenience (Fig. 318). The three rolls may be arranged 
relatively to each other in two ways. Two of the rolls may 
be fixed in position, both driven by power and with their 
axes in a horizontal plane; the third will lie above the space 



THE STEAM-BOILER. GENERAL CONSTRUCTION, 38 1 

betweeii the other two, or with its axis in the plane of the 
common tangent to the other two. This third roll will be the 
bending-roll, will have its axis adjustable, and will not be 
driven. Its position further from the lower rolls or nearer to 
them will determine the radius of the curvature of the plate 
(Fig. 319). The rolled and curved plate will gradually enclose 
the upper roll, so that if the bent edges are to come together 
the bearing or housing of this upper roll must be removable at 
one end to allow the completed cylinder to be removed end- 
wise (Fig. 318). This arrangement of rolls does not cause the 
plate to be curved all the way to the edges, which are parallel 
to the axis of the rolls, since a distance equal to the radius of 
the roll or more cannot receive the curving action of the 
upper roll with large diameters of cylinder (Fig. 319). A 
modification is to arrange the two driven rolls over each other, 
and to make the third approach the opening between them 
at an angle from below (Fig. 320). This arrangement brings 
the curving effect close to the edges, and has the plate posi- 
tively driven against the bending-roll by the nip of the two 
rolls which are driven. The only difificulty arises from a 
change of lengths of the contact surface as the cylindrical 
shape is developed. The two driven rolls would develop 
equal lengths as they revolve without slipping upon the 
shorter inner surface and longer outer surface of the curved 
plate. If this were not overcome, the driven rolls would 
exert a calendering action on a plate of sensible thickness and 
undo the curving effect of the third roll. The difificulty is 
met by driving one of the two rolls from the other by a dif- 
ferential or ** box " gear, by which the motion reaches the 
second roll from the first through a couple of pairs of bevel- 
wheels. The axes of one pair are independent of the fixed 
frame, so that if one roll has farther to move than the other 
the difference in path is able to be compensated by a motion 
of this movable axis which allows the gears to roll through a 
space while still transmitting the full driving effort necessary. 
The rolling process is effected by rolling the plate back 
and forth through the rolls with continuous adjustment of the 



382 MECHANICAL ENGINEERING OF POWER PLANTS, 




THE STEAM-BOILER, GENERAL CONSTRUCTION. 383 

third or bending roll until the gauged diameter of the cylin- 
der or segment of cylinder is reached. The rolls have to be 




Fig. 319. 

of diameter sufficient to withstand the tendency to flex, and 
of length sufficient to handle the longest or widest plate used. 
The rolls limit also the thickness of plate convenient for 
shells. Their convenient diameter imposes a lower limit for 



-B — - 




IE- 



Fig. 320. 

the diameter of flues to be made by their use. Their length 
imposes a limit upon the length of boiler-shell to be made in 
one piece, or in two pieces if the joint is to be longitudinal. 

209. Arrangement of Rings of Plate in Shells.— It is 
desired to have as few joints in the shell as possible, and yet 
the boiler must have a practical length. The least number 
of joints is reached in the arrangement shown for a shell 
boiler in Fig. 321, where the shell part is one long plate 
jointed lengthwise. The size of such boiler is limited by the 



384 MECHANICAL ENGINEERING OF POWER PLANTS. 

attainable size of single sheet both as to length and diameter, 
so that it is nnuch more usual to arrange the length of the 
plate circumferentially, and to get the necessary length by 




jointing such rings or zones by one, two, or more ring seams. 
In very large diameters, such as are usual in marine boilers, 
the rings themselves will each be made up of two or more 



THE STEAM-BOILER. GENERAL CONSTRUCTION, 385 

segments, jointed by longitudinal joints. In the ordinary 
shell of stationary practice the ring or zone is in one piece 
joined at the edges, and the usual diameter of such shells is 
fixed by the length of plate usually to be had. If there are 
three such rings or belts as in the usual iron boiler and in 
many steel boilers, these rings may be jointed to each other 
at the roundabout or ring seams in one of three ways. The 
three rings may be true cylinders, each a little smaller than 
the preceding, so that they fit inside successively like the 
joints of a telescope, and the larger laps over the smaller one; 
or one ring may be smaller than the other two (usually the 
middle one smaller than the two end ones), so that it will fit 
inside of both and form a lap (Fig. 431). The third plan is 
to taper each ring slightly, so that it will fit outside at one 
end over the end of the next ring. This end has the same 
diameter as the small end of that same ring, so that the two 
ends of the boiler are of the same diameter. The taper of 
the rings is laid out so that currents of hot gases or flames 
shall not impinge against the ends of such lapping ring-joints, 
but shall flow over the ridge which the lap makes. 

210. Heads of Boiler-shells. Flanging. — The head of 
the boiler-shell is that flat or arched surface which closes the 
two ends of the cylinder. It has to be jointed to the cylin- 
drical portion. American practice is to have the cylinder fit 
over the outside of the head, and to bend up the edges of the 
head all around to form a surface parallel to the cylindrical 
shell by which the joint can be made. This bending up of 
the edges of a flat disk to form a projecting ring or flange is 
called '' flanging." It may be done by hand or by machine. 
By hand the edge is heated locally, a sector at a time, and 
the hot metal is bent over the edge of a properly moulded 
anvil or former by means of heavy wooden beetles or mauls 
in the hands of skilled strikers or smiths. Wooden heads do 
not draw down the metal in bending as metal sledges would, 
and the blow is delivered over more surface. The objections 
to hand-forming are the cost of labor, the impossibility of 
uniform heating all round the edge, and the inaccuracy of the 



386 MECHANICAL ENGINEERING OF POWER PLANTS. 

final cylinder. Steel heads, forge-heated and hand-flanged, 
must be annealed after forming, since steel is specially sensi- 
tive to inequalities of heating, and the finished head unan- 
nealed is all distorted and unequally strained from this action. 
Hand-flanging must be so done that the steel never cools 
under treatment to its critical temperature, which is found at 
about a blue heat. It is brittle and liable to crack under the 
blows of even the wooden mauls. 

Machine-flanging is much to be preferred where practicable. 
It is usually a process of hydraulic forging with proper dies. 
When done at one process two cast-iron formers are used, 
one male and one female. The disk is heated uniformly all 
over, and when at proper temperature is laid upon the top of 
the hollow female die. The* male die descends concentric 
with the other by hydraulic pressure, and forces the plate to 
bend up uniformly all around and take the shape of the 
standard male former. The head is thus shaped at one heat 
to the required shape and diameter and without distorting 
strains. In other forms of flanging-press (Fig. 322) the 




Fig. 322. 



plate is held at a proper temperature between the faces of a 
hydraulic vise, while pressure comes radially upon the edge 
of the disk from hydraulic cylinders which carry shaping- 



THE STEAM-BOILER. GENERAL CONSTRUCTION. 38/ 

heads and bend down the edge gradually until the disk fits 
-the former which is the face of the hydraulic vise. 

Earlier European boilers will show the head jointed to the 
shell by a ring of angle-iron section, or by a ring of plate 
forged into that shape. The use of more ductile and superior 
metal for heads has made flanging more usual. 

The flange is usually placed inside the boiler. This keeps 
it protected from the rapid oxidation or burning to which 
projecting flanges would be exposed if hot gases or flame 
impinged on them and they were only cooled by conduction 
from the water at some inches' distance. 

Flanging stretches the metal right at the bend, but com- 
presses the metal beyond the bend which forms the flanged 
surface. The sharper the angle of the bend, the more severe 
these concentrated strains. Hence to bene flanges with a 
radius not less than four inches has been specified, to diminish 
this source of trouble. Flanging is also necessary in jointing 
rectangular fire-boxes and for the attachment of large flues 
to boiler-heads. 

211. Joints in Boiler-shells. Welding. — The rings which 
form the cylindrical shell of the boiler are curved from flat 
plates, and must be jointed at the edges and at their ends. 
The requisites of such a joint are: (i) strength to resist the 
strain from internal pressure; (2) tightness against leakage of 
water or steam, with a construction which shall not be too 
costly; (3) ability to withstand heat; (4) ability to undergo 
changes of shape from expansions and ntractions without 
injury to the metal. 

The two edges of the plate which are to be joined are 
arranged so as to lap over each other to be secured together, 
and this attaching can be done by welding or by some form 
of the rivet-joint. Bolting with a thread and nut will not 
ineet the second requirement of tightness against leakage 
unless the joint-surfaces are planed and finished and the bolt- 
holes reamed and the bolts turned. This is prohibitory from 
its cost; and even if this were not a barrier, the friction of the 
nut so reduces the clamping-power of the screw-bolt that it 



388 MECHANICAL ENGINEERING OF POWER PLANTS, 

would make a much weaker joint than is secured by the other 
plans. 

Welding of boiler-plate to make the joint with itself or 
other parts of the shell offers many advantages. The welding 
property of wrought iron and ductile steel enables them to unite 
at clean surfaces when pressed together with sufficient force 
in a state of sufficient plasticity from heat. The presence of 
oxide of iron or dirt or cinder between the contact-surfaces 
will prevent a satisfactory weld, or if there is no adequate 
pressure to unite the surfaces together. When welding is 
satisfactory it may be expected to be as strong as the rest of 
the metal — which has, in the case of wrought iron, been 
fabricated into plate by availing of the welding property 
through the entire course of manufacture. 

Welding of plate is done by lapping the two edges over 
for two or three inches, heating the lap to a welding heat on 
both sides by a flame or jet of gas free from sulphur or other 
oxidizing tendencies, and then bringing the lapped surfaces 
together either by the force of percussive hammer or sledge 
blows or by steady pressure of cams or roller-presses. Some 
fluxing material like borax which will make a fluid glass with 
oxide of iron may be used as a protection for the contact-sur- 
faces, so as to prevent oxidation from exposure to air, with 
the expectation that it will be expelled from the joint by the 
welding pressure, and carry with it everything which would 
interfere with good welding. 

Welding of boiler-joints offers these advantages: 

(i) It makes the joint as strong as the rest of the plate, or 
nearly so. 

(2) The plate is no thicker at the joints than elsewhere. 
This avoidance of a lap keeps the tensile strain from internal 
pressure always in the axis of the plate and without a ten- 
dency to flex at the lap or joint (par. 216). 

(3) Double or extra thickness is avoided at laps or joints. 
The plate gets unnecessarily hot at multiple thicknesses, and 
oxidation is more rapid there. 



THE STEAM-BOILER. GENERAL CONSTRUCTION, 389 

(4) No rivets are required, which makes the boiler lighter 
and less liable to leak. 

(5) A good welded seam is water-tight and requires no 
calking. 

The objections to the welded seam in boilers are: 

(i) It cannot be inspected for its satisfactory quality 
unless it is so bad as to allow water to leak through it under 
pressure. But it may be water-tight and yet be far from hav- 
ing full strength. While a test by hammer-taps to observe the 
resonance of the metal at the joint will reveal much to the 
practised ear, it lacks the convincing force of an inspection of 
each single rivet in a riveted seam. 

(2) Welded joints in large shells can only be gotten from 
a few firms with facilities and experience for such work. This 
has some effect upon the cost of such joints. But when a 
satisfactory welded seam can be obtained it makes an ideal 
joint. 

In cylinders with closed ends the last seam must be 
riveted even if the others are welded. The exception is 
where the head is flanged outward, or is convex inward so as 
to bring the closing joint outside the shell (par. 210). 

212. Riveted Joints for Boiler-shells. — When two plates 
are to be joined by rivets, they are lapped over each other, 
and through a hole which matches in the two plates a rivet 
is introduced red or white hot. This rivet has a head formed 
at one end in its manufacture, but the shank is straight. 
When in place through the holes, pressure is brought upon 
both ends of the rivet, whereby the projecting shank is upset 
and forced back upon itself, thereby enlarging its diameter in 
the hole until it fills it completely, and when the metal can no 
longer be displaced laterally in the holes, the metal of the rivet 
still projecting beyond the plate, spreads sidewise over and 
beyond the hole and forms the second head of the rivet. The 
rivet when completed has two heads connected by the shank 
which is still red hot when the head is finished, and which in 
its contraction on cooling draws the two plates together with 
a force measured by the modulus of elasticity of the rivet- 



390 MECHANICAL ENGINEERING OF POWER PLANTS, 

metal and by the cross-section of the shank. It is a force 
much in excess of that which any bolt and nut can exert. 

The riveted joint meets the requirements of a boiler-joint 
in that it is — - 

(i) Strong. 

(2) Water-tight. 

(3) Cheap. 

The difficulties which it introduces are: 

(i) The hole for the rivet cuts out just so much metal 
from the solid plate, and therefore the joint is not as strong 
as the plate where there are no holes. 



Fig. 323. 

2) In simple lap-joints the strain on either side of the joint 
is not resisted in the axis of the plate on the other. High 
pressure tends to flex the lap-joint till the two plates come 
into line (Fig. 323), and this flexure causes the deterioration 
called ''grooving " (par. 340). 

(3) The boiler-shell is thicker at joints than elsewhere. 

There are certain further disadvantages attending a badly 
made rivet-joint which will be noted hereafter. The design 
of special riveted joints is to diminish these difficulties. 

213. Construction of a Riveted Joint. Punching and 
Drilling. — The holes in the plate to receive the rivets may be 
made by punching, by drilling, or by punching out a small 
hole and enlarging it by reaming. Formerly, and with iron 
plate, punching was universal. More recently, and with steel, 
the latter methods are used. 

The punching of the hole is done in a punching-press 
(Fig. 324) in which a hard and tough steel cylinder comes 
down upon the plate supported upon an abutment or female 
die having a hole in it slightly larger than the punch (Fig. 
325). The punch shears its way through the supported plate 



THE STEAM-BOILER. GENERAL CONSTRUCTION. 39 1 

and extrudes a blank of the punched plate cut by its stroke. 
While at first the punch cuts the plate, after a fraction of an 
inch of penetration it tears its way through the rest of the 
thickness without true shearing action; and in a plate of 




Fig. 324. 

laminated structure such as wrought iron has, it is largely the 
reaction of the abutment or die which limits the lateral spread 
of the tearing effect. The extruded blank is conical, since 
the die is larger than the punch in order to free the latter 
and pass the blank. "^ The punching-presses may be crank- 
presses as shown, or the punch may be driven by hydraulic 

* Usually larger by y\j the diameter of the punch. 



392 MECHANICAL ENGINEERING OF POWER PLANTS. 

pressure. Flanged plates are usually punched in horizontal 
punching-presses. A spiral shape has been given to the 
impact-face of the punch so as to make the cut a gradual and 
progressive one around the circumference of the hole, and to 
help secure a true shearing action (Fig. 326). 




Fig. 325. 



Fig. 326. 



Drilling of plate is done by the ordinary machine-shop 
drill of two cutting planes meeting at an edge. Twist-drills 
are most convenient, although the flat drill is still to be met. 
The drill will be run by the ordinary drill-press. 

The gang-punch or multiple punch has a number of 
punches mounted in a fixed relation in a holder, so that one 
stroke of the holder punches two, three, or more holes at 
once and at a standard distance apart. 

Gang or multiple drills have a number of revolving spin- 
dles driven from a common source, each carrying its own drill 
and drilling a number of holes at once and at a fixed distance 
apart. These gang-drills usually drill alternate holes in a 
seam to permit a convenient distance between the spindles. 

214. Punching and Drilling Compared. — The objections 
to punching the holes for the rivets are: 

(i) The injury to the plate. This has already been 
referred to for a laminated material like wrought iron (par. 
213), but in steel the effect is different. The effect of the 
impact-pressure of the punch is to produce an effect upon the 
metal around the hole similar to that of hardening by heating 
and rapid cooling. The metal has its modulus of elasticity 



THE STEAM-BOILER. GENERAL CONSTRUCTION. 393 



raised, so that it stretches less before breaking or cracking, 
which is the same as becoming brittle and liable to fail in 
service under strain suddenly applied. Experiments would 
appear to show that the carbon of the steel enters into com- 
bination wth the iron under the shock, and, to restore the 
metal to the normal ductility after punching, the plate must 
be annealed. Otherwise the deteriorated metal must be 
removed by the reaming or enlarging of the hole until good 
metal is reached at a distance from the punched place beyond 
the effect of the blow of the punch. 

(2) The spacing of the holes is likely to be inaccurate in 
punching with a single punch, and when punched indepen- 
dently the holes in the plates which lap will not match, or 
will be '' half-blind " (Fig, 327). This difBculty arises when 
massive plates are presented by hand to the 
punch and the work is done too rapidly. 
The holes are laid out or are marked on 
the plate, and the punch mechanism thrown 
into gear when the mark is under the axis 
of the punch. Even when the punch has 
a "" tit " (Fig. 325) to serve to guide it to 
the axis of the hole it may seem to take 
too long to adjust the plate, and the stroke 
may be made before the setting was perfect. 




Fig. 327. 



Gang-punches 

avoid this trouble so far as each set is concerned, but best 
results are had from the use of feeding-tables on which the 
plate rests, and which are fed forward by racks or similar feed- 
devices, so that the plate moves each time through the same 
fixed distance, thus securing uniform spacing of the holes 
upon a line. Errors may creep in even here from a diver- 
gence laterally of the lines of holes which are accurately 
spaced lengthwise in two plates. Inaccurate spacing which 
causes the holes to come half-blind to each other must be 
corrected either by reaming out the holes till they do match, 
or by stretching them by the drift-pin to be referred to here- 
after (par. 219). If they do not match at all, the two holes 
are blind. 



394 MECHANICAL ENGINEERING OF POWER PLANTS. 

The objections to drilling the holes are: 

(i) With the single drill the process is slow. It takes 
from five to seven times as long to drill as to punch, or five 
or seven holes can be punched while one is being drilled. 

(2) This makes drilling costly unless gang methods are 
used. 

(3) The point of a drill is not a point, but an edge where 
two cutting planes meet. Hence the drill in starting has a 
tendency to work sidewise away from the true axis of its hole 
and follow one or the other of the corners of the edge-plane. 
If this tendency is disregarded, the holes do not come true 
except by accident. If time is taken to keep the drill start- 
ing true, the work is slow. 

(4) A drilled hole in thin plate usually has a burr or pro- 
jecting ridge raised around the edge of the bottom of the hole, 
where the feeding pressure on the spindle and drill forces the 
latter through the thin film of metal which remains in the hole 
after the point of the drill has come through, and cutting and 
resistance is at the edges only. This burr would prevent the 
joint of plates being water-tight unless it was carefully 
removed by filing. 

(5) The drilled hole is cylindrical; the punched hole is 
conical. It is an advantage to have the hole conical if the 
two small bases of the cones can come together (as at B in 
Fig- 33 0- The sloping sides give greater holding power to 
the head, and give a form of rivet better calculatd to prevent 
the head from snapping off in service. 

The points in favor of punching are its rapidity and cheap- 
ness. The points in favor of drilling are its harmlessness to 
the plate and the probable greater accuracy as to the match- 
ing of the holes. 

The plan of punching small and enlarging to size by ream- 
ing out the holes offers the advantage of rapidity and cheap- 
ness, and leaves no deteriorated metal. One-tenth of an 
inch of metal cut away from the edge of the hole will remove 
the hardened material, and such reaming is much more rapid 
than drilling out the solid metal. The reamer may be taper- 



THE STEAM-BOILER. GENERAL CONSTRUCTION, 395 

ing if conical holes are preferred. A great deal of work is 
done by this method, as combining the commercial advantages 
of one and the advantages as to quality offered by the other. 

Drilling, however, must be exacted for thick plates and 
large holes, and is best at all times. In the very highest 
standard of practice it is further exacted that the holes shall 
be drilled after the plates have been curved and assembled, so 
that the holes shall be drilled truly radial in both plates and 
with the sheets in place. This prevents troublesome burring, 
and prevents mismatching of holes. Special machines have 
been erected for this grade of work. 

215. Hand- and Machine-riveting. — The pressure neces- 
sary to upset the shank of the rivet into the rivet-hole so as 
to fill it and to form the second head can be exerted either 
by hand-hammers in the hands of skilled riveters; or a die or 
swage may be put over the end of the shank and struck by 
heavy sledges so as to upset the shank and develop the form 
of the die on the projecting end; or the pressure can be 
brought upon the rivet by a machine called a riveter or rivet- 
ing-machine. 

In hand-riveting, the rivet is pushed up from within 
wherever possible, and when in place a massive swage is held 
up against the inner head of the rivet by a helper with all the 
force possible, by leverage, while rapid blows are delivered 
upon the end of the hot shank by the riveters without. Hand 
-riveting is necessary for the closing seam of a shell in order 
that resistance to the heading of the rivets may be offered from 
within, and by the riveters' helper with his swage. The design 
of the shell must be such as to allow the ** holder-up " of the 
swage to get out of the boiler when the seam is completed. 
But machine-riveting gives so much better results in filling 
the holes by upsetting, and in forcing the plates to contact 
before the heat comes to press upon them and draw them 
together, that machine-riveting is used wherever practicable. 
Swage-riveting with sledges is better than light hammer-work 
with long or thick rivets, but is also less effective than the 
work of good machines. The compression of the machines 



39^ MECHANICA'L ENGINEERING OF POWER PLANTS. 

gives an added resistance to the joint by the frictional resist- 
ance which the pressure opposes to a sHding of the two 
plates upon each other. This resistance adds to the shearing 
resistance of the rivets by preventing the shearing edges of 
the plate from commencing on the rivet until the friction is 
overcome. 




Fig. 329. 
The usual types of riveting-machine are three: steam or 
air riveters, hydraulic riveters, and lever machines. In all types 
there will be a movable head actuated by power to compress, 
upset, and head the rivet against a fixed abutment or ''stake " 
which replaces the upheld " swage " in the hand of the helper 
in hand-riveting. This stake requires to be a stiff and power- 
ful organ of the riveting-machinq; and since the longer its 
length the more metal must be in it for strength and stiffness, 
it will be apparent that the stake limits either the diameter 
of flue which must pass oyer it, or the length of zone to the 
end of which the stake will reach; or it may limit both. The 
stake is fitted at its upper end with a die which fits the manu- 
factured head of the rivet (or else will reshape it), and the 
rivet is pushed through the hole from the stake side. The 



THE STEAM-BOILER. GENERAL CONSTRUCTION, ^97 

movable head is then allowed to exert its force endwise upon 
the rivet, upsets and heads it, and is then retracted. 

The steam-riveter shown in Fig. 329 has a piston of 
large area, which receives a relatively light pressure of steam 
or air upon each square inch of area, so that the necessary 
aggregate force is secured. The exhaust-steam after the 
working stroke comes round also to the front side, and is 
exhausted first from the working side so as to leave a pressure 




Fig. 330. 

to retract the piston before the exhaust occurs from the front 
side. The hydraulic riveter uses a plunger of small area, 
exposed to a water-pressure of considerable amount, perhaps 
250 to 350 pounds or more per square inch, so that a much 
less area under greater pressure does the same work as the 
large area under less pressure (Fig. 330). The lever or press 
riveters have an elbow-joint linkage which hangs flexed when 
the movable head is at rest, but can be straightened out by 
means of a cam or a third link, and in its straightening it 
compresses the rivet in its place against the stake with the 
great force of the elbow-joint combination. Some portable 
riveters are constructed on this principle with a fluid acting 



39^ MECHANICAL ENGINEERING OF POWER PLANTS, 

upon a piston to cause the elbow-joint links to straighten. 
Such are much used in bridge-shops and for girders. 

The hydraulic riveters are the most compact, but the high 
pressures used in them give trouble at the packings. They 
move more slowly than the steam-riveters in coming against 
the rivet end, and their effect is more that of pressure and 
less that of a blow. This latter is hard to prevent with an 
expanding fluid like steam, over which the valve exerts no 
control after it has been passed. Either of the fluid machines 
has the advantage over the lever machine that the pressure 
can be gradually increased to its maximum as the rivet yields 
and cools, and furthermore the pressure can remain upon the 
rivet an appreciable time. They have the further advantage 
over the lever type that the stroke or travel of the movable 
head is not fixed in length, but is fixed only by the refusal of 
the rivet to yield further to pressure. This is convenient 
when rivets of different length are in question for differing 
thicknesses or number of laps of plate. This has been met 
for the lever riveter by having the abutment-joint of the link- 
age mounted upon a bearing adjustable by a wedge for 
different lengths of rivet, or upon a yielding bearing which 
is, held to its seat by springs, or by heavy hydraulic pressure 
maintained by an accumulator. If the resistance offered by 
the stake to an upset of the rivet was too great as the linkage 
came straight, the back end of the linkage yielded and pre- 
vented such excess. It did not serve, however, if the rivet 
were shorter than the normal. Then the lever riveter does 
not get its full pressure upon the metal, while the hydraulic 
and steam riveters are not subject to this difficulty, but 
follow the rivet to refusal. 

The very intensity of the pressure in upsetting rivets by 
machine has sometimes caused the metal of the rivet to 
squeeze sidewise into the joint between the plates, wedging 
them apart and leaving a thin film between them. This is 
fatal to tightness of the seam. It is best to have a double 
ram construction, whereby an outer annular ram forces the 
two plates together as by a vise-pressure before the inner or 



THE STEAM-BOILER. GENERAL CONSTRUCTION. 399 

heading ram proper comes forward against the rivet. This 
closes the joint tight before the rivet begins to press upon it, 
and gives much the stronger and tighter joint of those 
made by machine. The use of such a riveting-machine is 
specified by some designers. 

The riveting-machines require adequate overhead hoisting 
appliances so that massive rings aad shells can be rapidly and 
•easily handled, and the joints and rivets presented truly in 
line and normal to the motion of the heading die. This jus- 
tifies a travelling crane in a busy shop. 

2i6. Design of a Riveted Joint. Strength. — The dis- 
tance from centre to centre measured along the line of the 
seam is called the pitch of the rivets. The pitch should be 
so chosen, when strength of the joint is the only consideration, 
that the shearing resistance of the metal in the rivets should 
be equal to the tensile resistance of that part of the plate 
"which remains after the holes have been made through which 
the rivets pass. If the pitch-length be taken as the unit 
length, it is obvious that the length of plate to be considered 
as resisting strain is the pitch less the diameter of the rivet 
chosen. The plate grows stronger as it becomes thicker, but 
the rivet does not, because its shearing area is determined by 
its area of cross-section alone. 

But a rational treatment of an ordinary boiler-seam for 
equal strength of rivet and plate is not profitable, because 
the primary requisite of tightness for the seam brings the 
rivets nearer together, or diminishes the pitch as compared 
with that required for strength only. Hence practice has 
iixed the usual proportions of rivet in relation to thickness of 
plate, and has fixed the corresponding pitch. (See Notes.) 

The machine-riveted seam can have a longer pitch than a 
hand-riveted one. The row of holes is usually distant from 
the edge of the plate a distance equal to one and one-half the 
diameter of the holes, so as to leave plenty of sound metal 
outside of the holes for both strength and stiffness and to 
be water-tight. It is obvious that if two rows of rivets are 
used, one behind the other, and with holes in line, a less 



400 MECHANICAL ENGINEERING OF POWER PLANTS, 

diameter of rivet may be used on each line with increased 
shearing resistance as compared with a single row, and yet the 
solid metal of the plate between holes can be increased with 
the same pitch. The whole intent of special designs of riveted 
joint is to bring the plate strength between holes up to the 
point at which the joint shall be as strong as the solid plate 
against tearing, while the "rivets shall have metal enough to 
prevent shearing. 

217. Rivets and their Arrangement. — Fig. 331 shows 
the conventional types of rivet in section. A has the conical 

A B C 




Fig. 331. 

head made by hand, the bottom showing the usual pan-tail 
which the rivet has as manufactured. B is the cup or button 
head resulting from the use of a swage. C ov A will represent 
forms given by the dies of riveting-machines. D is the 
countersunk head usual in shipwork or where a smooth skin 
surface is to be sought. 

Rivets of iron boilers should be of iron, and for steel 
boilers they should be of a mild steel able to stand the proper 
forge-tests. Their tensile strength is usualty taken the same 
as the shearing strength (or ^V o^ it), and may be put at 55,000 
pounds to the square inch for steel. The forge-tests are: 

(i) Bend double close when hot. 

(2) Bend to a U over a bar of its own diameter cold, and 
show no cracking in either case. 

(3) The head should hammer hot to form a disk 2\ times 
the diameter of the shank. 

(4) The shank should hammer cold to ? flat \ of an inch 
thick, and then withstand punching with a solid punch, making 
a hole of the size of the original shank; both of these without 
cracking or splaying at the edges. 



THE STEAM-BOILER. GENERAL CONSTRUCTION. 4OI 



For wrought-iron rivets the tensile strength may be 
called 50,000 pounds per square inch, and the shearing 
strength 40,000 pounds; the metal should withstand the same 
forge-tests. 

The arrangement of the rivets in a boiler-joint will be 




Fig. 332. 

either ordinary or special. The ordinary riveted joints are 
four: 

(i) Single-riveted lap. 

(2) Double-riveted lap. 

(3) Butt-joint with single cover. 

(4) Butt-joint with double cover. 

Figs. 332 to 338 illustrate these types. The lap-joint,, 
single- or double-riveted (Figs. 332 and 333), is very general 
because cheaper. Ring seams will be single- and longitudinal 
seams double-riveted (see par. 207). Double-riveted joints 



402 MECHANICAL ENGINEERING OF FOWER PLANTS. 




Fig. 334. 



THE STKAM-BOILER. GENERAL CONSTRUCTION. 403 

may be either chain or stagger as respects the arrangement 
of the rivets. In chain-riveting the rivets are behind each 
other in the two rows. The objection to the lap-joint is the 
tendency to flex the plates at the passage from two thick- 




FiG. 336. 

nesses to one when the pull on each plate seeks to oppose 
itself to that exerted in the line of the other (Fig. 323). The 
treble-riveted joint (Fig. 334) gives a longer lap and more 
plate area and more rivet-shearing area, as well as a stiffer 




Fig. 337. 

joint. The butt-joint with double cover (Fig. 338) doubles 
the number of rivets required as compared with the same class 
of lap-joints, but the strain is in line and without tendency to 



404 MECHANICAL ENGINEERING OF POWER PLANTS. 

flex the plates, and the rivets are in double shear. It is not 
so with the butt and single cover (Fig. 336). The double- 
cover butt is liable to have the outer cover overheated when 




Fig. 338. 

exposed to fire. The special joints are departures from the 
four conventional types, seeking to secure the features of the 
double butt with less expense. Figs. 337, 338, and 339 will 



THE STEAM-BOILER. GENERAL CONSTRUCTION, 405 



serve as types of such joints. The strength of single lap- 
joints being from 55 to 60 per cent of the original plate, and 
of double-riveted laps 70 per cent, such special double butt- 



^- 



-Q) 



r^>-^. 



■- -i-fer:i--e^.:.-:7£;t-e-^ 






— - — o — -,- — ^ e 



■-^ 



ci>-L-— •^- 



^ 



1 T '"'^J?' y^ 




-v4- 



Fig. 339. 

joints as Fig. 339 will show a strength of 85 per cent of the 
solid plate. 

218. Failure of the Riveted Joint.— While the riveted 
joint fails in one of two generic ways, either by shear of the 
rivets or by failure of the plate, the latter may occur in 
several ways. The rivet may {c) buckle or (e) shear the 
plate in tearing its way out, or the plate may crack and tear 





Fig. 340. 

(^) either between rivets or (^) between the rivet and the edge 
of the plate. The excess of rivet area to secure tightness for 



406 MECHANICAL ENGINEERING OF POWER PLANTS, 

the seam usually makes the failure occur in the plate (Fig, 
340). The danger from {c) occurs when hard steel rivets are 
used in soft iron plate; (e) may happen when the line of rivet-^ 
holes is too near the edge of the plate and the rivets are hard 
and dense. It is the least usual. The failure {b) is most 
common. The line between rivet-holes along the pitch is the 
shortest line or line of least resistance, and any maltreatment, 
of the plate in making the joint has tended to make it weaker. 
Such maltreatment may come from punching without ream- 
ing or annealing, whereby the steel is more brittle and less 
tough than it should be (pars. 213 and 214); or if the use of 
the drift-pin has been permitted, the metal has been initially 
strained locally thereby beyond its elastic limit. 

219. The Drift-pin is a tapering pin of hard and tough 
steel which is used to force and draw into coincidence two- 
holes in a seam which have not come opposite to each other. 
The taper pin is inserted in the half-blind holes and driven 
downward, so that it wedges the projecting edges of the holes 
over and draws the metal around the holes out of shape until 
the distorted holes agree. This will buckle the metal in front 
of the hole if the error in alignment is at right angles to the 
pitch, and cause failure (c), as well as strain the metal along 
the line of the pitch and start the crack which ends in failure 
(U). If the error in alignment is along the line of the pitch, 
the drift-pin tends to start failure (^) and injures the plate 
between rivets, which renders it liable to failure {U) also. 
The drift-pin is fatal to good metal in steel boilers, and its use 
should be forbidden by the specifications. If holes must be 
expected to be inaccurately spaced, the coincidence should 
be brought about by use of a cutting-reamer, whereby no 
injury to the material is incurred. Drilling the holes in places 
makes both drift and reamer unnecessary. 

The failure of the joint by gradual action of over-pressure 
by methods (c) and (e) is apt to show itself by leakage before 
it is imminently dangerous. Inspection may also reveal 
failures {p) and {d) if they are not the result of some sudden- 
strain. It is an element of safety in the riveted joint that it 



THE STEAM-BOILER. GENERAL CONSTRUCTION. 407 

should give warning of its probable failure by the leakages 
which accompany the first stages of such failure. Old seams 
may fail from corrosion or grooving by other methods than 
these, determined by the character of the deterioration which 
has weakened them. But except where the solid plate is 
weakened by corrosion or grooving, such wear and tear is 
most apt to hasten a failure at one of the four weak points 
above discussed. 

220. Stays and Staying. — It has been seen (par. 202) that 
the sphere and the cylinder are the only forms which have no 
tendency to change shape under internal pressure. Or, in 
other words, that the circular is the limit form towards which 
all sections tend, and which they will assume if the elasticity 
of the material will permit such deformation of section to 
occur without breaking. When it is inconvenient to use 
cylindrical or spherical elements in the design desired, and 
particularly where flat surfaces are to be used, the tendency 
to deform under pressure must be resisted by positive means 
other than the tensile or transverse strength of the material. 
Rods, bolts, bars, or braces used to prevent such deforma- 
tions of flat or arched or non-circular surfaces are called by 
the general name of ''^ stays,'* 

The simplest case is where two parallel surfaces, flat, or 
parallel with one concave and the other convex to the pres- 
sure and not far apart from each other, are to be tied together 
to resist the pressure between them which tends to force them 
apart. This occurs at the sides of the fire-box in locomotive 
boilers, in some marine and upright boilers, and at the crown- 
sheets of some designs of locomotive boilers. The most ready 
solution is to tie the two surfaces together by round bolts or 
rods whose area of cross-section shall be sufficient to resist 
the pressure upon the area they support, and for which the 
distance between centres shall be so small that no deflection or 
bulging of the plates can occur between them. With thinner 
plate this centre distance used to be four inches in locomotive 
practice; recent practice raises this distance to six inches or 
over. These stay-bolts are either headed over hot on the 



408 MECHANICAL ENGINEERING OF POWER PLANTS. 

outside of the two plates, like an ordinary hand-made rivet, 
or more usually the holes in the two plates are threaded and 
the stay-bolt is screwed into both plates, and is slightly upset 
on the ends when in place, to prevent working out and leak- 
ing, and also to reinforce the strength of the threads. 
Thicker plates give sufficient length of thread for strength. 
Hollow stay-bolts are also used on the water-legs of locomo- 
tive boilers, both because they will manifest the beginnings 
of failure by leakage of steam through the crack of the initial 
fracture, and because the air which goes through the hollow 
keeps them cool and helps supply oxygen for the fire. The 
simple heading of the stay-bolt like a rivet was troublesome 
on account of the tendency of the shank to bend, and also 
because an unequal contraction of the group of stay-bolts 
made some too tight and others loose. The holes for the 
screwed stay-bolt are tapped by a long tap so that both 
plates have their threads parts of the same screw, and the two 
plates are under equal tension if all bolts are of the same 
length. This method is most satisfactory if the stay-bolts are 
short and of equal length. As they heat by contact with the 
steam or hot water they lengthen and slack their hold, and 
the longer they are the more they yield. Hence, while this 
same method can be used to stay the two flat cylindrical 
heads of a cylindrical shell boiler to each other and prevent 
their bulging outward, it is usual only for boilers of compara- 
tively short length, such as are used in marine practice, or 
unless the pressure is to be so high that no other plan seems 
advisable. Such/' through-stays" will be of round rods of 
sufficient size, threaded at the two ends, which have been upset 
so that the bottom of the thread on the enlarged ends shall 
have a diameter equal to that of the body of the rod. The 
hold of the rod in the plate by its thread is reinforced by a 
nut on the outside which caps over the end of the rod, and a 
flexible copper washer between the plate and the nut helps to 
make the joint water-tight, A jam-nut on the inside with a 
washer helps to keep all snug, and prevents its \vorking loose 
by expansion and contraction. Since through stay-rods of this 



THE STEAM-BOILER. GENERAL CONSTRUCTION. 409 



type cannot usually be put close together, but must be spaced 
far enough apart to allow a man to pass between them for in- 
spection and for work, their centres will be sixteen inches 
apart at least ; so that they must each withstand the pressure in 
such case exerted over an area of 256 square inches, and it is 

1 




^^^5^^ 



usual to stiffen the head by means of angle- or channel-irons or 
similar structural shapes, whereby the holding power of the 
stays shall be distributed over the more flexible head. This 




Fig. 342. 

can also be done by large washers on the outside of the head. 
Fig. 341 will show the detail of such through-stays. 

To avoid the threaded hole in the heads and the project- 
ing end of the stay, the stay-rod has been fastened to stay- 
bars on the heads by a pin-joint. Fig. 342 shows a form of 



4IO MECHANICAL ENGINEERING OF POWER PLANTS, 

this method where the stay-bars are relatively heavy forgings 
of two to two and a half inches square, with lugs bump-welded 
on the inside. The stay-rod ends in a fork which spans the 
lugs, and a bolt or pin connection ties the bars together upon 
the two heads. Somewhat lighter than this is the similar 
arrangement of Figs. 343, 344, and 345, where angle- or tee- 




Fig. 343. 

irons are riveted to the head, and the stays pinned to them by 
pins in single or double shear; but in these arrangements the 
obliquity of the stay-rod indicates a prevalent arrangement for 
medium pressures. The inner end of the stay-rod in this case 



THE STEAM-BOILER. GENERAL CONSTRUCTION, 4ir 




Eb==^ 




Fig. 344. 




Fig. 345. 



412 MECHANICAL ENGINEERING OE POWER PLANTS. 



is fastened to the cylindrical shell at a convenient distance back 
from the head by rivets, and thus the bulging tendency is 
withstood by the tensile strength of the shell lengthwise, in 
which direction it is abundantly strong. Instead, again, of 



O 



O 



nx 






structural ?ron bars, single or independent sockets may be 
used as in Figs. 346 and 347, whereby the action of the stays 
is distributed even more generally over the surface to be 
stayed. Fig. 345 will serve for detail of these also. It is 
apparent that the diagonal stay must be stronger than the 



THE STEAM-BOILER. GENERAL CONSTRUCTION. 413 

straight one to withstand the same strain (Fig. 353). The 
cheapest and most uncertain of the diagonal stays is the plain 
rod, flattened at both ends as Fig. 346 is at one end, and 




riveted by such flattened ends to head and to shell. Modern 
practice does not favor these by reason of the uncertainty as 
to their holding capacity, and would limit them to very low 
pressures or exclude them entirely. 

Gusset-stays are a form approved for heavy pressures in 
British practice. Triangular or trapezoidal pieces of boiler- 



414 MECHANICAL ENGINEERING OF POWER PLANTS. 

plate are riveted to angle-irons on the head and cylindrical 
shell and bind them into a rigid structure. The stays do not 
come close to the corner of head and shell, so that in cutting 
away the heel of the right-angled triangle the fourth side 
may become parallel to the hypothenuse of the original 
triangle. The stays are usually placed radially upon the head 
(See Figs. 402 and 445). 

Where a fiat surface has no surface parallel to it to which 
it can be directly stayed, and the length is too short for wise 
use of diagonal bracing, the surface must be made stiff by 
A B 



Frd. 353. 
bars acting by their stiffness like girders to prevent deforma- 
tion or collapse. This is met in the flat crown-sheets of 
locomotives and in combustion-chambers of marine boilers. 
The problem is complicated by the intense heat upon such 
surfaces, which precludes the use of solid bars, which would 
keep water from the metal. 

The crown-bar method is shown in Fig. 430, in which the 
bars appear in pairs, running across the flat sheet from side to 
side of the furnace. The sheet is stayed to these bars by 
J-inch bolts which pass up through the plate and between the 
two bars of each pair. The joint between head and plate is 
made by a copper washer, and the washer under the nut 



THE STEAM-BOILER, GENERAL CONSTRUCTION. 415 

serves to bind the bars together. A taper washer or distance- 
piece keeps the bars from the plate, so as to cause water to 
touch as much plate as possible, and keep the plate flat when 
the bolts are tightened. The deflection of these bars is pre- 
vented by sling-stays when they are long, or their own resist- 




FiG. 349. 

ance to bending is depended on if they can be short. Figs. 
348 and 349 show other methods, used either where the 
crown-sheet is arched to approach parallelism with the outer 
shell, or where the outer shell is made flat to become parallel 
with the flat crown-sheet. The stay-bolts have taper surfaces 
under their heads, which draw into tapering reamed holes in 



41 6 MECHANICAL ENGINEERING OF POWER PLANTS. 

the sheet by the pressure of the steam, and copper washers 
under the head help to secure tightness. Fig. 349 is called 
the Belpaire fire-box. (See also Fig. 432.) 

Staying should not be too rigid, and it is very objection- 
able to have a flexible and a rigidly stayed surface attached 
to each other. The motion of the flexible part either from 
heat-expansion or by pressure produces a great strain or a 
concentration of the deformation at the margin where these 
tendencies to move and to resist motion meet. This is what 
tends to shear stay-bolts, and to weaken joints or plates by 
grooving at the edge of the rigid area. 

221. Manholes. — In the construction of riveted shells a 
provision must be made to allow the helper to get out who 
has ''held up " for the final riveting of the last joint. Access 
must also be had to the inside of the boiler for inspection 
when in service and for repairs. The function of this hole is 
thus to let a man in and out, and is for this reason called the 
manhole. It should be as small as possible to effect its pur- 
pose, because the metal of the shell removed to make it is 
just so much strength removed from the boiler. Measure- 
ments show that the average man is fourteen inches on the 
axis of the longest dimension through the articulations of the 
hip-joints with the pelvic bone. The shoulder dimension, 
though naturally larger, is flexible and contractile, and any 
man can pass through a hole through which his hips will pass. 
The dimension at right angles to the line through the hip- 
joints is normally less than the other, and is a flexible one 
when it is not less. Hence the manhole receives an elliptical 
shape with its lorig axis 14, 15, or 16 inches long, and its 
short axis 9, 10, or 1 1 inches, or four or five inches less than 
the other. This elliptical shape has furthermore a very prac- 
tical advantage, in that the lid which is to cover the hole 
and must have a size larger than the hole, so as to lap over 
the edges, can be made to fit upon the inside of the hole and 
can yet be itself passed through the hole from without. The 
lap over the edges must be less than one half the difl^erence 



THE STEAM-POILER. GENERAL CONSTRUCTION. 41/ 

between the long and short axes of the elliptical hole. If the 
hole must be circular, the lid has to be external. 

The lid is held to its seat over the manhole when internal 
partly and mainly by the pressure upon its inner side; but to 
make the joint steam-tight, and to hold it from displacement 
at other times, the lid has one or two studs symmetrical upon 
its long axis, which pass up through a proper hole or holes m 
a bridge or '' dog" of cast or wrought iron which spans 
the manhole-opening, so that when the nut is screwed down 
upon the stud and bears on the outer surface of the dog, the 
lid is drawn to its place and held firmly by the nip of the 
dog upon the edges of the hole (Fig. 350). The joint between 




Fig. 350. 

the lid and the plate is made tight by a gasket of rubber or 
asbestos-board or similar material whose compressibility shall 
compensate any inaccuracy of contact-surfaces. It is rare that 
finish of surfaces can be secured or maintained which will 
make a true metal-and-metal joint without gasket under the 
conditions prevailing around a manhole. The hole cut in the 
plate of the boiler leaves the strength less than when the metal 
was solid, at the zone whose width is the span of the hole. 
All the circumferential strains in the ring of plate are trans- 
ferred around it till at the edge of the hole they are balanced by 



41 8 MECHANICAL ENGINEERING OE POWER PLAA^TS, 

no counteracting force except that supplied by the reluctance 
of the material to split into filaments by yielding sidewise. 
The tendency can be illustrated by a band of elastic material 
like rubber with a hole punched in it. Under strain length- 
wise the hole becomes deformed, and most so at the ends or 
at the points farthest from the solid material at the sides of 
the hole. Hence it is desirable not only to place the hole, 
if in the shell, with its short axis lengthwise, but also to 
reinforce the weakened plate around the edge of the hole; 
and this practice has given rise to manhole mouthpieces or 
nozzles. The simplest form is a forged ring of wrought iron 
(more desirable than a similar ring of cast iron) riveted around 
the edge of the hole in the plate. The lower surface will be 
plane to form the flat seating for the cover, while the upper 
surface conforms to the shape of the boiler. The rivets are 
in countersunk holes on the face of the seating, or else the ring 
is broad enough to allow the line of rivet-heads to come 
beyond the lap of the cover. Such ring resists the tendency 
to flex which will occur when the manhole is upon a cylin- 
drical surface and metal has been cut away which would 
maintain the shape when the pressure came upon the contin- 
uous ring of plate. Fig. 351 shows the ring made of a 




C C 

Fig. 351. 

flanged plate riveted within the shell, and Fig. 352 the 
exterior nozzle arrangement. The interior seating offers 
some advantages from the resistance to flexure which it offers. 




Fig. 352. 
The location of the manhole will be either upon one of 
the heads, or upon the head of the dome of the boiler, or 
upon the shell, or upon that attachment called the mud- 



THE STEAM-BOILER. GENERAL CONSTRUCTION. 419 

drum. On the cylindrical or spheroidal surfaces of shell or 
dome or drum, seatings or nozzles are a necessity, to secure 
planes for the covers to seat themselves upon ; on fiat surfaces 
they are desirable for strength and stiffness. The construc- 
tion of the boiler may require more than one manhole, a 
condition frequent in marine practice. 

222. Hand-holes, as their name indicates, are smaller 
openings in the shell to give access to the hand for an inspec- 
tion by touch, or for convenient cleansing or minor repair. 
The construction is the same as for the manholes, the 
reinforce or seating being of boiler-plate or a flat ring of 
wrought iron. Their location and number will be determined 
by the design of the boiler in order to serve their purpose 
and leave no corner which inspection cannot reach. 

223. Edge-planing and Calking. — The shearing of the 
steel plates to size has left an edge or selvedge of metal which 
is brittle and unreliable from the effect of the shearing-planes. 
This deteriorated metal should be planed away by a cutting- 
tool. Fig. 354 shows such an edge-planer for plate, the 
sheet being held by the clamping-screws as in a vise, while 
the tool traverses along the edge. It is convenient to give 
the edge a bevel in planing, which is not only of service for 
appearance' sake, but gives an edge at the lap or joint to be 
used in calking the seam. 

Calking is done by upsetting the lower edge of the 
bevelled sheet into the joint by means of a round-nosed chisel 
held against the edge and struck with a hammer. Fig. 355 
shows the method of calking with a round-nose tool, which 
is much to be preferred to the sharp-nosed chisel, although 
the latter is easier to use. The sharp corner of the sharp tool 
may indent the lower plate at the joint, and thus start the 
first crack whose ultimate consequence will be the weakening 
of the plate at that point, which the illustration suggests. 

224. Sundry Details of Construction. — The expanding of 
tubes, the stiffening of flues, the dome, the mud-drum, and 
other special details of construction will be referred to under 
proper headings with the special types of boilers to which 
they particularly belong. 



420 MECHANICAL ENGINEERING OF POWER PLANTS. 



11 



fe i 



li 




CHAPTER XX. 

TYPES OF BOILERS. EXTERNALLY-FIRED SHELL 
BOILERS. 

225. Classification of Types. — The most convenient divi- 
sion of types of boilers makes two great classes. The first 
group includes the externally-fired boilers in which the furnace 
or fire-box is outside of the vessel which contains the steam 
and water under pressure, and is provided for in the setting 
of the boiler. The second group includes the internally- fired 
boilers, in which the furnace or fire-box is within the pressure- 
structure which surrounds it either on all sides, or on all sides 
except the bottom. This salient difference gives rise to the 
most easily followed lines of study of the types. Another 
division whose significance will appear makes the two classes 
consist of the shell boilers and the sectional boilers; another 
scheme would put the marine boilers in one class, the loco- 
motive boiler and its derivatives in the second class, and those 
types most frequently met in land or factory practice would 
make the third class. The division into externally- and 
internally-fired boilers will be followed, and within that first 
class the subdivision into shell and sectional types, and within 
the second class the division according to use or purpose. 
This will give rise to the following table: 



Externally fired class: 

Plain cylinder boilers 

Cylinder flue " V forming shell boilers. 



I 



Cylinder tubular ** ) 
Sectional boilers. 

Coil boilers. 

Sundry types. 



421 



422 MECHANICAL ENGINEERING OF POWER PLANTS, 

Internally-fired class: 

Cornish, Lancashire, and Galloway boilers. 

Locomotive and upright boilers. 

Marine boilers. 

Water-tube boilers and field-tube boilers. 
Sundry types. 
226. Plain Cylinder Boiler. — The plain cylinder boiler is 
historically the first successor of the earlier spherical boilers 
(called the haystack and balloon types) in England, and is 
the fundamental form of shell boiler from which the others 
have been derived. Between the spherical and the cylinder 
boiler came the wagon boiler of James Watt (Fig. 360), in 
which the surfaces were arched or convex inward. This con- 
struction favored the formation of the lateral flues for the 
passage of gases, according to the plan of splitting the column 
of hot gas or flame at the bottom and rear of the boiler, and 
having the hot gas touch the boiler all along the sides as well 
before passing out to the chimney. This horizontal turn of 
the gases was called the '' wheel-draft " system. The con- 
cave surfaces were not adapted to withstand high pressures, 
because they tended to pass into the cylinder under internal 
pressure. 

The cylinder boiler is supported between two parallel 
brick walls at a distance apart just equal to the diameter of 
the cylinder. The fire or furnace is at one end of the space 
between these walls, and the flame and hot gases surround the 
entire lower semi-cylinder up to the horizontal diameter, and 
transfer the heat from the combustion of the fuel by radiation 
and by contact to the metal of this semi-cylinder, and from 
this by contact and convection to the water which fills this 
part of the shell. The heads of the boiler may be either flat 
or hemispherical (egg-ended is the usual name), and may either 
be exposed to hot gases or not. The gases and flame will 
escape from the combustion-chamber behind the bridge-wall 
to the chimney-flue and so into the atmosphere. The bridge- 
wall forms the rear of the furnace. Fig. 361 will present a 
typical cylindrical boiler. 



TYPES OF BOILERS. 



423 



It is apparent that the cylinder should always be more 
than half full of water, or that the water-line should be above 




Fig. 360. 

the horizontal diameter, in order that when the water fluc- 
tuates below its normal level there should even then be no 



424 MECHANICAL ENGINEERING OF POWER PLANTS, 

surface of the shell exposed to overheating, because exposed 
to flame or hot gas on one side and without cooling water 
on the other. This feature will be found common to all 
externally-fired shell boilers. Furthermore, it is not advisable 
to fill the boiler with water much above the horizontal 
diameter, since it is apparent that the free surface of the water 
diminishes as the boiler is filled. This free surface is that 
from which the bubbles of steam-gas generated by heat 




Fig. 361. 

escape into the space above the water. It is called the 
*' disengagement-area " for steam, and it is important that it 
should be large. If too much steam must escape from too 
small an area, the rising steam-gas keeps the surface of the 
water bubbling and frothing. The steam lifts the top layers 
of water, so as to give a fictitious indication of level of water, 
and entrains with it a proportion of water in drops or mist or 
even in some mass in its too rapid flow from the surface of 
the water to the outlet-pipe. Such a foaming or frothing is 
to be avoided, and the boiler which sends water into the 
steam-pipe is said to '' prime." The presence of a scum of 
dirt or of grease increases the tendency to foam and prime, 



TYPES OF BOILERS. 425 

because the steam-gas forces its way out by bursting through 
this scum, but to carry the water-level too high is not only 
to bring the disengagement-surface nearer to the pipe-outlet 
for steam, but it is also to diminish its area. A boiler forced 
to evaporate faster and disengage more steam than at its 
normal rate will also be likely to foam and prime. 

The accepted standard for early practice was to make the 
volume filled with water (called the water-space) to be two 
thirds of the volume of the boiler, while the space in which 
steam is confined above the water (called the steam-space) 
should be the remaining one third. This was reached by 
making the area of the head to be divided by the water-line 
into segments whose area was as 2 is to i. 

This was an empirically correct ratio, based on observa- 
tion, but lacked a rational basis, because the real store of 
steam is not in the steam-space, but in the heated water. A 
more satisfactory basis is the disengagement-area basis, and 
experiment has shown that when the flow of steam from the 
water into the steam-space is at a rate such that it would fill 
the steam-space three times a minute, the disengagement was 
slow enough to give no trouble from priming. This experi- 
ment was made on a marine boiler, and trouble was found 
from entrained water when the evaporation had to be so rapid 
that the steam-space was filled five times per minute; at four 
times per minute trouble was occasional but not continuous. 
Stated otherwise, a linear velocity of flow of steam faster than 
2 feet per second through the water surface will entrain water 
with the steam. The larger the cylinder-volume to be filled 
per stroke, or the greater the number of strokes per minute, 
or the greater the volume of steam required per minute, the 
larger the aggregate steam-space required if pressure is not 
to be allowed to fluctuate when the disengagement-rate is 
normal and slow enough to prevent priming. 

227. Domes and Steam-drums. — The difficulties in the 
engine-cylinder from entrained water have been referred to 
(pars. 161, 198), and the methods of getting rid of it. But 
most boilers are arranged specifically to diminish the danger 



426 MECHANICAL ENGINEERING OF POWER PLANTS. 

from excessive priming by helping to remove its cause. The 
dome which appears on most shell boilers is an upright cylin- 
der of boiler-plate of some considerable diameter, up to two 
thirds that of the shell and so attached to it as to form part 
of the steam-space or an addition to it. In horizontal boilers 
it will have its axis at right angles to that of the boiler, and 
will be attached to it by flanging the sides of the dome out- 
ward, and curving the sides so as to fit the curvature of the 
top of the shell (Fig. 362). The shell is cut away under the 




Fig. 362. 

dome in the type form to the full diameter of the dome. 
The steam-outlet will be a pipe passing from the top of the 
dome or near it. 

It will be apparent that the dome accomplishes three pur- 
poses: 

(i) It removes the inlet to the steam-pipe farther from 
the disengagement-area than it could be if it were on the 
shell directly; water is less likely to spatter or be projected 
into the steam-outlet. 

(2) The linear velocity of steam is low in the large cross* 



TYPES OF BOILERS. 



427 



section of the dome. Entrained water is less likely to be 
carried at low linear velocities than high, and it has time to 
separate out from the steam by Its greater specific gravity. 

(3) The steam flows to the dome from a larger proportion 
of the disengagement-area than it would to a small neck or 
nozzle on the shell. Under a neck or nozzle the water is 
heaped up (Fig. 373), and the greatest disengagement occurs 
at that point, a condition favorable to priming. The dome is 
usually put at that point on the length of a boiler at which 
experience shows the disengagement to be most active, so 
as to avail of this action, and to prevent injury caused by a 
disregard of the tendency there. 

The objections to the dome are the weakening of the shell 
from the cutting away of the metal under the dome, whereby 




Fig. 363 

not only is the strength affected, but the cylindrical shell 
tends to flatten under the pressure, and tnis results in leakage 
at the dome-seam at the top. The shell is an unstiffened 
curved stay v/here the hole is cut, and the double thickness 
of the lap of the dome-joint does not replace the strength of 
the unbroken cylindrical surface. Hence the dome-joint is 



428 MECHANICAL ENGINEERING OF POWER FLAA TS. 

further stiffened, either by turning up the plate into a vertical 
flange, or by a stiffening-ring, as was described in manhole- 
seatings (par. 221). Fig. 363 illustrates these methods. 

This objection to the weakening of the shell by the hole 
for the dome has induced designers to seek to secure the 
functions of the dome without such cutting of the shell. 

(i) The shell has been perforated with either many small 
holes or one larger one under the dome, but not cut away 
entirely (Figs. 364 and 369). The area of the holes should 




Fig. 364. 

aggregate several times greater than the area of the pipe. 
The objection to this is that the tendency to straighten is not 
removed, because the pressure in the dome balances the 
pressure below the perforated surface, and there is no ten- 
dency to keep the cylindrical shape. The plate acts like a 
curved stay only. Moreover, the dome cannot be used as 
a means of entry to the boiler, unless the hole in the shell is 
the full size of a manhole, and the top of the dome does 
make a convenient place to enter and to place the manhole. 
(2) To attach the dome by a neck (Figs. 365 and 371). 



TYPES OF BOILERS. 



429 



The flanges of the neck return some strength and stiffness to 
the shell. It is more convenient, if this is to be done, to 
make the dome a horizontal drum (Fig. 373). 

(3) To use a horizontal drum or pipe of large diameter 
overhead, to which the boiler will be connected by a neck if 
but one boiler is used. This plan is specially convenient 
where several boilers are side by side or in a ''battery," as 
it is called. All can deliver into a common drum, and from 




Fig. 365. 
this a drainage-connection may remove any entrained water 
which may be carried through neck or nozzle by high velocity 
of steam-currents. Fig. 367 will illustrate this arrangement 
when the drum is transverse, and is really a large pipe merely 
jointed to each boiler by piping which allows of expansion 
without cross-strain. (See also Figs. 373 and 406.) 

(4) The use of a dry-pipe with perforations. Fig. 368 
will show this arrangement. The steam leaves the disengage- 



430 MECHANICAL ENGINEERING OF POWER PLANTS. 




TYPES OF BOILERS. 



431 



ment-surface to pass into the steam-pipe through a number 
of small holes in the interior pipe which is a prolongation of 
the steam-pipe inside the boiler. The gentle current into 
each opening prevents entrainment of water, because the 
aggregate area of openings is in excess of the area of the pipe. 
The objection is the stoppage of the inlet-holes in muddy 
waters. This is an arrangement used in marine practice and 
in some locomotives. The weight of the dome is an objection 
on board ship, and an elevation of the centre of gravity of the 
boiler, and on some locomotives the dome has been objected 
to because, in addition to its other drawbacks, it stands in 
the way of the view of the engineman. Where the locomo- 




FiG. 368. 



tive-boiler has a dome the throttle-box will be near its top, 
and the pipe to the cylinders runs down through the steam- 
space. With a perforated dry-pipe the throttle-box will be 
at that end of it at which it comes out through the front head 
of the boiler. 

(5) A form of separate dome has been used for marine 
.boilers on smooth waters in which the dome is an annular 
cylinder and has the smokestack-flue pass up through it. 
This has prevailed in river-boat practice, and was particularly 



432 MECHANICAL ENGINEERING OF POWER PLANTS. 

convenient in wooden hulls, because the ** steam- chimney,"' 
as such dome was called, could get no hotter on its outside 
than the heat of the steam. The dome was high, and the 
effect of the hot chimney-gases within it was to dry or even 
to superheat the steam in the annular space (Fig. 384). 

Dome-heads are sometimes made of cast iron for moderate 
and low pressures. The greater thickness of metal required 
with cast iron is convenient for attaching manhole-fixtures, 
valves, and pipe-outlets, and the dome-head is not exposed 
directly to heat nor to sudden changes of temperature. The 
unreliability of cast iron (par. 203) is still against it even 




Fig. 369. 

here. Flanged wrought iron or steel is better and will be 
generally used, and will be universal for high pressures and 
large diameters, especially where staying must be done 
(Fig. 369). 



TYPES OF BOILERS, 433 

228. Conditions Suggesting the Use of the Plain Cylin- 
der-boiler. — The plain cylinder-boiler offers advantages to be 
weighed against those to be urged for its derivative forms 
when the following conditions have preponderating weight: 

(i) For a given length and diameter, or space covered in 
ground-plan, the plain cylinder-boiler holds the most water. 
Water has the highest value for its specific heat, or a given 
weight or volume of water will hold more heat stored in it 
than anything else except some chemical solutions. Hence, 
when heat is to be reserved in a boiler, to meet sudden and ex- 
cessive demands for heat and steam for a short while, the great 
weight of heated water will give up this stored heat, and will 
supply much steam, with but a slow fall of pressure as steam 
is withdrawn. On the other hand, if the steam is regularly 
drawn, but there are periods when heat is insufficiently sup- 
plied or is supplied in excess, the weight of water gives out 
steam without calling at once for more heat to keep up pres- 
sure in the first case, and absorbs and stores the excess in the 
second case, without rapid and perhaps dangerous rise in 
pressure. In other words, the storage capacity for heat in 
the mass of water keeps the pressure uniform under varia- 
tions in demand for steam and in supply df heat. This 
property of the cylinder-boiler makes it a safe type, and has 
made it a preferred type in iron-making plants where waste 
gases are used to heat the boilers. The gases vary widely in 
heating effect, both from varying quantity and composition. 

(2) The cylinder-boiler, being all open within and free from 
perplexing corners where cleansing would be difficult, is 
adapted for use in places where the water to be evaporated 
contains salts or mineral matter which will be precipitated on 
the shell of the boiler upon boiling, and will remain behind 
when the pure steam-gas is withdrawn. The cylinder-boiler 
is more easy to clean than any of its derivatives. 

(3) The cylinder-boiler does not compel the products of 
combustion (flame particularly) to pass into or through flues 
where their temperature is so lowered that chemical union 
with oxygen is prevented or delayed. The relatively cool 



434 MECHANICAL ENGINEERING OF POWER PLANTS, 

metal of the boiler-shell only meets the hot gases where the 
latter are in considerable volume. Hence the cylinder-boiler 
is of advantage with gas as fuel, which makes a long flame, or 
with oil, or with such coals as, having a large proportion of 
volatile constituents, burn with a long flame — which will be 
one of over sixteen feet in length. There is no limit but con- 
venience to the length of a cylinder-boiler, and it can be so 
long that the flame may burn completely and still keep im- 
parting heat by radiation to the shell, while if the flame is 
compelled to intimate contact with the cooler metal the flame 
is extinguished, and the carbon remaining unburnt appears as 
lamp-black in the current of hot gas, and smoke from the 
chimney shows that carbon has been wasted. 

229. Objections to the Plain Cylinder-boiler. 

(i) The large weight of water makes it slow in getting up 
steam. 

(2) It is not a rapid-steaming boiler in the sense that a 
given ground-plan does not give a large heating-surface to 
supply a large weight of steam in a unit of time. 

(3) To utilize the heat of a hot furnace the boiler has to 
be long, so that when the gases leave the boiler-setting to 
pass to the chimney they shall have parted with all available 
heat. The hanging of a long boiler is either dangerous or 
troublesome if strain is to be avoided, as will be discussed in 
paragraph 266. 

These difficulties, which are practical ones and real, have 
put the cylinder-boiler at such a disadvantage, as compared 
with its derivatives, that it will only be used where its dis- 
advantages are outweighed by its offering some paramount 
advantage. 

230. The Elephant or French or Union Boiler. — Under 
these several names are included derivatives of the plain 
cylinder-boiler in which two or more cylinder-boilers are 
superposed in the same setting, the several components being 
joined by vertical necks or nozzles. In the elephant boiler 
the two cylinders have the same diameter, the lower one 
being usually the shorter. In the PVench boiler there may 



TYPES OF BOILERS. 



435 



be one or two lower cylinders. In the union boiler the 
lower cylinder is apt to be the larger, and may have tubes 
through it, and, in place of the separate necks, the boilers may 
be united along their whole length. Fig. 370 shows the short 
elephant type or *' double-decker," and Fig. 371 the French 
arrangement. Fig. 372 shows the long elephant boiler for 
blast-furnace use, with the lower cylinder on a grade to help 
circulation and drainage. 




Fig. 370. 

The elephant or superposed arrangement increases water- 
storage, and therefore heat storage, with a given diameter of 
shell for each cylinder, and without increasing ground-plan 
area. The smaller diameter of the cylinder makes it safer 
against rupture. Heating-surface is also increased. The 
objections to the type are the uncertainty of the circulation 
of steam-bubbles and hot water within the two cylinders, 
since the steam formed in the lower boiler must reach the 
•disengagement-surface and the steam-space by ascending 



43^ MECHANICAL ENGINEERING OF POWER PLANTS, 




TYPES OF BOILERS. 



437 



through the same necks down which must come the water to 
replace the steam which has been made. Fig. 373, which is 
drawn to show the circulation in a boiler with a steam-drum 
and two connections, will illustrate this point. A second 
difficulty is from the unequal expansion of the upper and 
lower boilers, which concentrates its effect at the necks or 
nozzles, straining them and causing them to leak. These 
types have been much more important than they are now. 

231. Mud-drum. — The use of the cylinder-boiler with 
impure waters has given rise to the use, with this type and 
with many others, of the appendage called the mud-drum. 
It is intended to catch and hold precipitated solid matter in 




Fig. 373 
the water of the boiler, and keep it if possible from settling 
upon parts of the heating-surface where its presence would 
do more harm. Hence the mud-drum will be an inverted 
dome or a drum at the bottom or coolest part of the boiler, and 
connected with it by a neck or nozzle in line with those cur- 
rents of circulation within the boiler which will direct descend- 
ing solid matter into the drum ; with the view that, when once 
within the drum, the absence of circulation therein would 
prevent any mud or like material from coming out again. 
The mud-drum is therefore withdrawn from contact with hot 
gases by encasing it in brick, or by having it where the gases 
only meet it when cooled by contact with other parts of "the 
boiler. Fig. 431 shows the mud-drum B with an axis 
-oarallel to that of the boiler. It is often transverse to the 



43^ MECHANICAL ENGINEERING OF POiVER PLANTS. 



boiler in other forms. It usually has a manhole-opening, and 
from it the blow-off pipe is attached, so that mud can be 
blown out by opening the valve with pressure within the 

i 




boiler. The feed-pipe delivering fresh water to the boiler 
sometimes enters the mud-drum, but this is not the best 
place. 

The mud-drum in pure waters often reduces to a very 
small appendage or disappears entirely. The difficulty with 



TYPES OF BOILERS. 



439 



it occurs when care has not been taken to guard against its 
expanding at a different rate from that of the boiler itself, 
because cooler, while rigidly attached to the latter and not 
free to move. This brings strain at the connecting neck or 
necks, followed ultimately by leakage and by corrosion at 
those points. 

232. The Cylinder Flue-boiler. — In order to avoid an 
inconvenient length of boiler and yet cool the furnace-gases 
as far as possible before allowing them to escape to the chim- 
ney, these gases may be taken at the back of the boiler after 
having traversed the bottom of the shell, and brought to the 
front of the boiler by means of flues made of proper conduct- 





Fig. 374. 

ing material and passing from head to head through the 
space heretofore filled by water in the cylinder-boiler. The 
effect is to increase the heating-surface in a given ground-plan 
and to secure more effective cooling of the flame or hot gas 
by a transfer of its heat to the walls of the flues which are 
cooled by the water which surrounds them. The gases turn 
upward in a space at the rear head of the boiler, which will 
be called the ''back connection," and from this space enter 
the flue or flues. 

In externally-fired flue-boilers there will be usually two, 
three, or five of these flues, if of large size, traversing the 



440 MECHANICAL ENGINEERING OF POWER PLANTS. 




to 

CO 

6 



TYPES OF BOILERS. 44 1 

water-space. They will be made of boiler-plate, riveted or 
welded, or (if not of too large diameter) of lap-welded boiler- 
tube. The necessary length of flue will be secured by joining 
lengths together either by lap- or butt-joints riveted, by weld- 
ing, or by the upset- or bump-joint (Fig. 374), in which one 
tube is enlarged enough to receive the end of the other. But 
the length of the flue-boiler is limited by the convenient 
length of such flues. 

The joint with the heads will be made by flanging the 
edges of a hole inward until the proiecting flange will permit 
the flue to be riveted to it, with the flue inside of the flange 
(Fig. 375). The flange might be turned outwards if the gases 
were never to be hot enough to overheat the projecting ends 
of flange and flue, which will only be kept cool by conduction 
from the metal which touches the water (Fig. 379). The 
metal of the flange made on the head is inside the water in 
the other arrangement. 




Fig. 376. 

The flue is exposed to the pressure in the boiler with a 
tendency to be crushed inwards or collapsed by such pressure. 
A cylindrical flue of small diameter and homogeneous struc- 
ture ought to be strong to resist collapse, but a local over- 
heating combined with the effect of the weight of the flue 
itself often tends to produce a local deformation, after which 
the areas exposed to pressure are no longer equal and collapse 
proceeds rapidly. To strengthen large flues against this 
tendency they are usually built with stiffening-rings around 
them in the water which keep them cylindrical to pressure, 



442 MECHANICAL ENGINEERING OF POWER PLANTS, 

or they are corrugated ringwise with the same object. These 
stiffening-rings are either plain rings with light pressures, or 
else the ring receives a greater transverse resistance by being 
made of angle or tee iron (Figs. 376 and 377). The distance- 




FiG. 378. 

pieces or thimbles keep water in intimate contact with the 
flue-metal, to guard against overheating. Fig. 378 shows two 
joints for the rings which have more flexibility for freedom of 
expansion than is given by positive joints, and this is an 
advantage which they offer. The flue and shell of the boiler 
need not be nor remain at the same temperature, and will 
therefore have different lengths, tending to push or pull upon 
the heads and flex them back and forth if the flues and shell 



TYPES OF BOILERS. 



443 




444 MECHANICAL ENGINEERING OF POWER PLANTS. 

are both rigid. The strength given by corrugation will be 
referred to under internally-fired boilers, in which such corru- 
gations are more frequently applied. 

233. Uses and Application of the Cylinder Flue-boiler.— 
The flue-boiler will be used with advantage in the same con- 
ditions as the plain cylinder-boiler. It is adapted for con- 
venient use with bad feed-waters, and for fuels having volatile 
matter or gas which burns with a long flame which the flues 
are large enough not to extinguish. The flues have diminished 
the amount of water which the boiler holds (Fig. 379), and 
so the pressure will fluctuate more rapidly, but the flue-boiler 
makes more steam than the cylinder-boiler, and more rapidly. 
Until the advent of the sectional types it was the ironworks 
type of boiler, and with many feed-waters it is still. 

234. The Cylinder Tubular or Multitubular Boiler. — 
If the hot gases are passed through the water-space of the 
boiler in a large number of small tubes, instead of by a small 
number of larger flues, another type of boiler results. The 
difference is only in size of tube and the fine subdivision of 
flue-gases which results. A tube of seven inches in diameter 
or over is a flue before the law, and a flue of less than six 
inches in diameter becomes a tube. 

The small diameter of the tube makes it necessary to 
fasten the tubes to the heads by a special process called ex- 
panding, which is discussed below. 

The diminished size of the tubes makes it possible to get 
in a great number of them through the water-space, thus 
enormously increasing the heating-surface, but in horizontal 
boilers it is not desirable to crowd tubes into the water-space' 
unduly, nor to make them of too small size. If made too 
small, the friction of the gases may prevent the proper draught 
through them. If too near together, they impede the circula- 
tion of the water (see Fig. 373) and the convection of heat, 
and prevent the free and rapid release of the steam-bubbles 
formed at the bottom and among the tubes. If grouped too 
close to the shell, they preclude inspection and cleansing of 
the shell. Best modern practice groups the tubes in two nests, 



TYPES OF BOILERS. 445 

separated by a vertical space between them where there are 
no tubes, and no tube in either nest comes nearer to the 
curve of the shell than four inches. The bubbles and circu- 
lation-currents rise in the middle space, and the descending 
currents go down in the four-inch spaces at the sides. 

The tubes may be arranged in vertical rows at the same 
time that they are in horizontal rows, or they may be stag- 
gered, so that the tubes in one row are beneath the spaces in 
the row above and below it. The staggered arrangement gets 
in the greatest number of tubes, but is not so favorable ta 
free circulation of water and steam-bubbles among the tubes, 
and no access is possible to lower rows of tubes for cleansing 
or for scraping off of scale. 

Tubes should not come nearer together than three 
quarters of an inch, and one inch or more is to be preferred. 
If the tubes must be staggered, it is better to make the 
horizontal spacing greater than the vertical spacing so as to 
favor circulation, and this is advisable if convenient even 
with the all-vertical rows. 

235. Boiler-tubes. — The usual boiler-tube is of lap- 
welded wrought iron or steel. It is manufactured from care- 
fully selected stock, and carefully sized as to its external 
diameter, by which its nominal size is determined. The 
length of such tubes is either twelve or sixteen feet, so that 
tubular boilers are apt to be designed to be either eleven or 
fifteen feet long to prevent waste. It is not convenient to 
have the tube much more than sixty diameters in length. It 
is inconvenient to joint such tubes unless one length of tube is 
quite short. For short and costly boilers for high pressures 
drawn steel tubes have been used which have no seam, but 
have been reduced from a solid ingot by drawing over a man- 
drel. These are coming into increasing use as the manufac- 
ture of assured and satisfactory quality of tubes of proper size 
becomes more general. Brass and copper tubes have been 
much used in fire-engine-boiler practice by reason of their high 
conductivity for heat. They introduce, however, a tendency 
to a galvanic action in the boiler, under which the iron ele- 



44^ MECHANICAL ENGINEERING OF POWER PLANTS. 

ment suffers corrosion. The aggregate cross-section of the 
tube-openings in a boiler has been called its calorimeter, and 
with natural draught it should be equal to or a little greater 
than the cross-section of the chimney-flue into which the tubes 
deliver. The accepted proportion for this latter area is one 
eighth of the area of the grate under the boiler on which the 
coal is burned. 

236. Ribbed Tubes. Serve-tubes. Retarders. — A 
special form of boiler-tube has been used to some extent, 
which is fitted with ribs lengthwise, or is thickened at several 
points of its inner circumference (Fig. 380). The object of 
this is to arrest more completely the available heat in the hot 
gases flowing through the tube, so that from this extra metal 
the heat may be abstracted by conduction. A somewhat 
similar function is discharged by what have been called re- 
tarders in the tubes. A cross-shaped bar the length of the 
tube is laid within the ordinary cylindrical tube, and absorbs 
heat from the gases, which it transfers to the tube by radiat- 
ing such absorbed heat, as well as acting to retard the too- 







Fig. 380. Fig. 381. 

rapid flow of gas at such a rate as would prevent complete 
transfer of heat to the tube. 

An objection to the ribbed tube is the difficulty in cleans- 
ing it when the gases deposit a sticky residue on the cooler 
surface of the metal. The retarders are cleansed by being 
taken out. 

237. Expanding of Tubes. — The tubes of a tubular boiler 
require to be fastened securely and water-tight to the two 



TYPES OF BOILERS. 



447 



heads — sometimes called the tube-sheets. The process is 
Icnown as ''expanding." 

The heads are drilled with properly spaced holes, of a size 
just to admit and pass the tube. Hence comes the necessity 
for a standard dimension for the exterior diameter of such 
tubes. The holes are usually drilled by a lip-drill (Fig. 381) 
or tit-drill, in which the central nipple is guided by a smaller 
hole first drilled in the axis of the larger hole. The pilot 
hole is more easily drilled in its true position than the larger 
one, because the cutting-planes of the small drill come to a 
smaller edge at its point, and less trouble and time need be 
taken to keep the drill to line in starting. The hole made, 
the tube is passed through, and when in place the tool called 
a tube-expander is inserted within it and at the proper dis- 
tance. Types of the expander are shown in Fig. 382, 




Fig. 382. 

In the roller form three rollers are borne upon segments 
which guide them, and upon which radial pressure can be 
brought by the central conical or tapering pin. When the 
rollers inside the tube are opposite the tube-sheet or just 
behind it, upon the inside of the tube, the rollers are forced 
outward and revolved inside the tube. The rolling pressure 
causes the metal of the tube to flow outward until the resist- 
ance of the hole in the tube-sheet is encountered. Then the 
tube and the hole are pressed to fit each other (Fig. 383) with 
a force usually sufficient to be steam-tight and having a very 



448 MECHANICAL ENGINEERING OF POWER 

considerable strength. To prevent the tube and its sheet 
from sliding under changes of length due to temperature, the 
end of the tube is slightly turned over or upset — called bead- 
ing — so as to grip the outer face of the tube-sheet. This 
both adds to strength and serves to prevent leakage. The 
beading is usually done with a special form of swaging-chisel, 
often called a '* thumb-swage " from the shape of its pressure 
end, which has a longer prong which enters the tube, while 
the shorter prong projects over the annular tube end, and 
gives an aspect suggesting the combination of index-finger and 
thumb on the human hand. 




Fig. 383. 

There are other forms of tube-expander, acting by weag- 
ing or direct pressure, but the roller form takes less power 
and gives better results. The fit of the expanded-tube is a 
pressure and frictional one. Hence any tendency to push or 
pull the tubes through the tube-sheet (from heat or from 
yielding to pressure) causes the expanded tubes to leak in 
their holes. With high pressures a certain proportion of the 
tubes — one in five, often — are made of extra-heavy stock, so as 
to allow for a greater strength due to the more efficient head- 
ing or beading of the thicker metal. Or, again, with thicker 
stock in the stay-tubes, the outside which projects beyond the 



TYPES OF BOILERS. 449 

sheets can have a thread cut on it, upon which a stay or lock- 
nut will be screwed home, and thus convert the tube into a 
through-stay. Such stay-tubes will be located where the ten- 
dency of the heads to flex under the pressure needs partic- 
ularly to be guarded against. 

Expanded tubes can be re-expanded so as to be made tight 
if leakage should be developed by service; but this cannot 
be done very often, since the metal must undergo a pressure 
in expanding which transcends the elastic limit of the material 
(otherwise it would spring back when the expander was with- 
drawn), and as the result the tube is apt to crack when the 
process is overdone. 

238. Staying of Tubular and Flue Boilers. — The tubes 
and flues-serve not only to tie together the two heads or flue- 
and tube-sheets to which they are fastened, but they also 
serve to lessen the pressure on these surfaces because the area 
occupied by them can have no pressure upon it. Hence in 
such boilers the staying will be limited to the upper segments 
of the heads and above the water-line. 

The water-line will be so adjusted to the top of the tube- 
or flue-surface that there shall always be at least three inches 
of water above the tubes or flues even when the water-level 
has descended to the level considered the danger-point. The 
method of staying may be any of those discussed in par. 220. 

239. Uses and Application of the Cylinder Tubular 
Boiler. — The great heating-surface in a compact form and the 
efiflciency with which the numerous tubes extract the heat 
from the currents of hot gas, have made the tubular boiler the 
type which will be usually met where it can be wisely used. 
It is therefore almost a standard for the externally-fired type. 
It presents the following features: 

(i) Great heating-surface in a small space. 

(2) This gives it ability to make steam rapidly, and a great 
deal of steam from a given area of ground occupied, as com- 
pared with the preceding forms. 

(3) This evaporative capacity is cheaply bought. The 
tubular boiler is not an expensive one, but is the cheapest of 



450 MECHANICAL ENGINEERING OF POWER PLANTS. 

the efficient types, costing under ordinary commercial condi- 
tions from $8 to $11 per horse-power. 

(4) The water is subdivided by the tubes into small 
masses, securing immediate transfer of the heat of the metal 
of the tubes to all parts of the volume of water. Hence the 
boiler responds promptly to an attempt to force it. 

As objections to the tubular boiler may be advanced: 

(5) The water-space is so filled with tubes that access to 
the lower parts for cleansing is difficult, and to some places 
is impossible. This objection is a fatal one if water is to be 
fed to the boiler which has great amounts of salts in it which 
are precipitated on boiling. 

(6) The fine division of the gas-currents in the small tubes 
will so lower their temperature that they are extinguished. 
If the flame would naturally be longer than the length from 
the furnace to the entry to the tubes, the extinction of the 
incandescent particles on lowering the temperature makes the 
gases smoky, and carbon is wasted as soot. The fine sub- 
division in tubes is also fatal to further union of carbon with 
oxygen, and combustion, if not completed before the gases 
enter the tubes, will either be incomplete, or else will tak-e 
place beyond the boiler at some possibly inconvenient place 
— such as the top of the stack or at its throat. 

It is these considerations which have made the multi- 
tubular boiler the prevalent type with anthracite or other 
short-flame fuel, and with the pure waters of New England. 
Its advantages have made it desired even where flaming fuels 
and poorer water would point to the use of the flue types. 



CHAPTER XXI. 

TYPES OF BOILERS. EXTERNALLY-FIRED SECTIONAL 

BOILERS. 

240. Definition of a Sectional Boiler. — A sectional boiler 
is a steam-generator in which the plan of a single enveloping 
shell to contain the water and steam is abandoned and is 
replaced by that of a number of small generating vessels so 
joined together that the steam formed in all of these separate 
units or sections is delivered from a common disengagement- 
surface into a common steam-space. The sectional principle 
may be carried in a boiler of large capacity to the extent of 
subdividing the disengagement-area, so that the steam from 
several such areas shall be delivered into a common steam- 
drum, from which it shall be withdrawn by the steam-pipe. 

The discussion of par. 202 would suggest that these units 
or sections should either be spheres or cylinders or combina- 
tions of either. Practice confirms this, and the convenience 
and other advantages of the cylinder (which when of small 
diameter becomes a tube) will be found to give to most of the 
sectional boilers a tubular character. From the definition, 
however, these tubes will contain the water within them, and 
will have the heat applied on the outside. This fact makes 
them often known as *' water-tube " boilers in contradistinc- 
tion to the shell tubular boiler, which has its tubes " fire- 
tubes," and the water is outside of them but within the 
enveloping shell. The Harrison sectional boiler is the only 
type of importance based upon the spherical unit. All the 
others will be found to be water-tubular. 

241. Advantages of the Sectional Principle. — The sec- 
tional principle offers certain advantages irrespective of the 
method followed by the builder in carrying it out. 

451 



452 MECHANICAL ENGINEERING OF POWER PLANTS. 

(i) By subdividing into sections each section has a small 
diameter, or one much less than that of the shell of the 
shell boiler. Strength to resist rupture with a given internal 
pressure increases as the diameter is less (par. 207). Hence 
each section is far safer against rupture than the large shell 
with same thickness of metal, and the danger from explosion 
of the boiler is much more remote. 

(2) The rupture or failure of any one of the units from 
overpressure or deterioration from any cause should not and 
usually does not cause the failure or loss of the whole struc- 
ture. The failure of the unit should act as a safety feature, 
whereby pressure is released at one place only and before the 
other units are involved in any serious overstrain. Further- 
more, the repair of any unit or section makes that part as 
good as new, and in this way the parts of the boiler may be 
gradually replaced and the whole structure become really 
new. It is, therefore, the safety of this type of boilers which 
has given it the great development of recent years as the 
pressures of steam have been increasing. The safety is not 
from the avoidance of all possible harm which a rupture may 
entail. The injury from escaping steam or hot water may be 
as fatal in either case. But the sudden release all at once of 
the enormous energy stored in the water of a boiler is much 
less likely to occur, and the train of disaster is avoided which 
would usually follow in the case of a similar failure of a large 
shell. 

Since the great reduction in diameter which comes when 
the units are tubes would give unnecessary strength if the 
same thicknesses were used, it is more common to have 
thinner metal for the tubes. Hence follow: 

(3) Lighter weight for a given evaporative capacity. 

(4) Thinner tube-metal in the fire- or gas-currents makes 
rapid transfer of heat to the water to be evaporated, so that 
the heating-surface is efficient, or a less number of feet of 
heating-surface becomes permissible, though not always ad- 
visable. 

(5) The sectional construction makes the boiler portable 



I 



TYPES OF BOILERS, 453 

and manageable so as to be put conveniently in places where 
access is difficult. The shell boiler must be handled as a 
whole, or built in place, if the doors or openings in walls are 
not large enough to pass it in or out as a whole. Sectional 
boilers can be put under finished buildings, or can be shipped 
beyond rail or water transportation and there assembled. 

(6) Repairs and renewals are easy, cheap, and rapid, and 
can usually be made by available labor and skill, and entail 
but a short stoppage of the plant. 

(7) The mass of the boiler which receives the action of 
flame and heat is less than in shell boilers. 

(8) Sectional boilers can be driven further above their 
nominal capacity than shell boilers. In the horizontal tubular 
type such driving may be carried a little over 10 per cent; in 
sectional types it may be over 50 per cent excess, and even 
for a while as high as 100 per cent. 

242. Disadvantages of the Sectional Principle. — The 
sectional principle, however, offers certain disadvantages, also 
irrespective of the method followed in applying it; but the 
degree in which any given form suffers from them may be 
different. 

(i) The aggregation of units must be connected together 
steam- and water-tight under pressure. Unequal expansion 
(or contraction) of different parts or units must strain or 
loosen these joints, or flex or distort those parts whose length 
is changing, or wrench those to which they are attached if 
rigidly fitted to them. Efforts to mitigate this evil have 
given rise to the curved tube for the unit, instead of the 
straight tube, and underlie some forms of flexible connections 
for the units. 

(2) The small unit principle precludes the idea of imme- 
diate personal access to the inside of the tube-surfaces for 
cleansing and inspection. This must be reached in some way 
or other in any form of generator which is to be properly 
called a safety-boiler. Hence there has resulted a prevalence 
of straight-tube units, to which access can be had from the 
end through a proper cap or hand-hole lid, and there is usually 



454 MECHANICAL ENGINEERING OE POWER PLANTS. 

a cap at each end, in order that inspection of the inside of 
the tube may be made with the eye at one end of the tube 
and a Hght or torch or candle at the other. The cap feature 
is also a necessity if a tube is to be renewed without dis- 
mounting adjacent ones. 

The objection to the cap feature is the multiplication of 
joints, which must be faced or ground joints so as to be tight 
without gasket or packing, and which are an occasion of 
leakage, and therefore of corrosion, when not attended to most 
carefully. The multiple-joint objection belongs also to some 
types which have no caps 

(3) The necessity for combining the evaporation of several 
tubes or units into one common duct or header, which is 
present in most of the types, makes the effective disengage- 
ment-surface become only that part of the water-surface which 
is -near the outlets of these headers. The disengagement is 
therefore tumultuous at such points when the boiler is driven, 
and water-gauges applied near such parts show a fictitious 
water-level ; and if the steam-outlet has to be near such part 
of the drum, the boiler is likely to prime. 

(4) The circulation of the currents of water in any boiler is 
due partly to the presence of steam-bubbles, which are lighter 
than the hottest water, and partly to the action of the less 
warm water, which is heavier than the hottest water. In a shell 
boiler this circulation is untrammelled by any narrow passages 
where high velocity is called for. In the sectional types the 
circulation must be determinate; and if all units are to be full 
of solid water, the descent of cooler water must be just as 
fast and positive as the ascent of the steam-gas bubbles to the 
surface of disengagement. Where friction or scale or bad 
design prevents this free descent of heavier water, and where 
steam formed in the units displaces water but cannot itself 
escape to the steam-drum, the unit becomes overheated and 
oxidizes and corrodes, and its overheating lengthens it unduly 
and produces the difficulties discussed above under (3). 

Defective or impeded circulation with waters which deposit 
scale causes the scale to settle in the tubes or units, causing 



TYPES OF BOILERS. 455 

them to overheat and lengthen and produce the same 
trouble. 

(5) Since the water is within the tube or unit, with press- 
ure on it, the failure of such tube or unit compels the whole 
structure to be put out of use for the repair. When a fire- 
tube fails, a plug of pine wood can be fashioned for each end 
and securely driven home from without. The leakage swells 
the wood and keeps it tight, while preventing the wood from 
burning further than a protecting thickness of charcoal on the 
outer surface. Such plugs will last for months if a shut-down 
is inconvenient. 

Furthermore, where tubes are attached in nests or groups, 
the repair to a middle one can only be done by removing 
those tubes which are outside or around it and which may 
not need to be removed for any other reason. This consid- 
eration has dictated the prevalence of the straight-tube type 
arranged in essentially parallel rows, and with free space irt 
the line of the tubes endwise. 

(6) Tubes or units which are so shaped or fitted that thejr 
cannot be inspected inside by the human eye for their entire 
length, or which are so curved that cleansing by scraper is 
uncertain or even inconvenient, are to be objected to or con- 
demned outright, for many conditions if not for all. 

(7) The gases pass too rapidly through the necessarily 
limited length of the tubular units, and leave the setting at 
too high a temperature, without having given all their avail- 
able heat to the water. 

(8) The workmanship and parts of the sectional boiler 
make it costly, per unit of capacity, as compared with the 
fire-tube shell boiler. While prices vary, the sectional is apt 
to cost from one and one half times to twice as much as the 
shell boiler, or from $11 to $18 per horse-power, with an 
average of $14 or $15 in large sizes. 

243. Classes of Sectional Boiler. — The sectional-boiler 
principle may be attained in many ways, but they will group 
themselves for examination into a small number of classes. 

First, the units may be spherical or tubular. There are 



45^ MECHANICAL ENGINEERING OF POWER PLANTS, 



% 






^^jyjiiELUj^LiaijjiM 






TYPES OF BOILERS. 



457 



few examples of spherical units; the other class is more prev- 
alent. 

The tubular class may include: 
(i) Straight tubes. 

(2) Tubes curved at ends, straight in middle. 

(3) Tubes curved for their whole length. 

(4) Closed-tube types. 

The straight-tube class may have the tubes inclined at 
about 15° from the horizontal, or inclined from the vertical, 
so that they are sometimes called, respectively, horizontal or 




Fig. 386. 

vertical tubes; and the curved-tube classes pass into the coil 
type when the curvature becomes continuous for any one tube 
for more than 360°. 

These several types in practice are identified by their 
builders' or originators' names. The predominance of one 
type over another is so often in any one locality a matter of 
business enterprise or commercial achievement, and the im- 



45 8 MECHANICAL ENGINEERING OF POWER PLANTS. 



provements on each type are so much conditioned upon a 
leading personaHty in each period of use, that it becomes 
unsatisfactory to treat of the individual types by name or at 
length. Certain typical forms alone are presented. 



-17^10-- 




-16^6- 



Fig. 387. 
244. Spherical Unit Type.— Figs. 385 and 386 show a 
sectional boiler built up of spheroids of cast iron in earlier 



TYPES OF BOILERS. 



459 



forms, and latterly of steel castings of Bessemer metal. These 
each have circular openings which fit similar openings in the 
units above and below them, making a metal-and-metal rabbet- 
joint. The series of units is tied together lengthwise and 




Fig. 388. 
crosswise by wrought-iron tie-rods, which come out through 
the cap which closes the last openings in any series. These 
tie-rods not only provide the strength to resist the tendency 



460 MECHANICAL ENGINEERING OF POWER PLANTS. 

to separate, and furnish a flexibility for the connections, but 
also under excess of strain they will stretch enough to cause 
the joints of the units to leak and relieve some of the pressure. 
The wrought iron also gives to the cast-iron whole some of 
the properties which cast iron would lack if used alone or 
altogether. The boiler has some surface in the steam-space 
exposed to hot gases, which gives a superheating area which 
tends to dry the steam when the boiler is working slowly. 
It offers some of the disadvantages discussed in par. 242. 

245. Vertical Tubular Type. — Figs. 387 and 388 show 
two types of the vertical tubular arrangement, one with 
straight tubes and the other with curved ends. The curve 
is introduced so that unequal expansion may flex the tube, 
and not work the tube in the fixed tube-sheets into holes in 
which its ends are secured by expanding. The tubes inclined 
from the vertical pass their steam-bubbles from each tube 
directly into the upper drum, and water from the lower drum 
supplies each tube directly and freely. This is the great 
excellence of these types — the great volume below and above 
the tube ends, and the independent disengagement from each 
tube at the top. Both violate some of the principles laid 
down in par. 242, particularlv that concerning repairs to a 
middle tube, and many tubes in the process of curving become 
of unequal thiclcness from the curving pressures. 

246. Horizontal Straight Tubular Type. — Figs. 38Q to 
395 present longitudinal sections and details of prevalent 
types of water-tube boilers with nearly horizontal tubes. It 
will be seen that the tubes are expanded, in series or sets, into 
headers. These headers are of cast iron or of wrought steel. 
Each tube has opposite to it an opening large enough to pass 
a new tube when renewal is necessary, and through which 
inspection and cleansing is done. This hole is covered by a 
cap in some forms, but in Fig. 395 the cap is replaced by a 
short connecting-tube whereby the individual header is 
coupled to its neighbor, instead of being in one piece with it. 
The spherical joint and the pressure-ring make the joint tend 
to tightness however the length of any individual tube may 



462 MECHANICAL ENG 7JVF.FRING OF POWER PLANTS. 




TYPES OF BOILERS. 



463 



vary. Fig. 392 shows the cap on the outside. If the hold- 
ing-bolt breaks from overscrewing, the cap blows outward 

5 




Fig. 395. 




Fig. 396. 

with great energy and releases hot water in a four-inch stream. 
Ficr 3q6 shows an inner plate which will be forced outward 



4^4 MECHANICAL ENGINEERING OF POWER PLANTS. 

against the opening if the holding-bolt breaks, and tend to 
hold back the rapid flow of hot water. 

The length of the descending pipe at the back of the boiler 
gives the descending energy to the cooler and denser water, 
while the water in the inclined tubes and front header is 
mixed with steam-gas and is also hotter. Hence the circula- 
tion should be determined by this arrangement. The mud- 
drum is coupled to each of the back headers at their bottom 
so as to catch descending solids which the current may propel 
beyond the tube-openings. The steam- and water-drum 
furnishes disengagement-area. The steam-outlet from it 
should be towards the rear and away from the higher water- 
level which prevails at that place when the front headers dis- 
charge into it. Fig. 391 shows a type in which separate 
headers are avoided and their joints, but the tubes are 
expanded into true water-legs at a fixed distance apart. 
Cleansing or renewal is done through holes in the outer plate 
of the leg, covered by caps. 

247. Closed-tube Types. Field Tubes. — It has been 
sought by many designers to use a tube as a unit which shall 
be closed at the bottom, and shall open at its top into the 
water-drum in which lies the disengagement-surface. The 
tube requires to be of sufficient diameter that the ascending 
current of steam-bubbles shall not interfere with the descend- 
ing current of water, and this double action seems best secured 
when the tube-unit is inclined about 15° from the vertical. 
Then the bubbles formed in the tube ascend continually along 
the upper elements of the tube, and the lower elements (which 
are those turned to the fire and against which the hot gases 
impinge) are always bathed by the descending water. This 
was a feature of the Allen boiler (Fig. 397), and although it 
suffered from, the difficulty of repair to middle tubes, it has 
been a favorite idea among German designers. If, however, 
the tube is of small diameter, and ebullition is too violent or 
the tube too nearly vertical, the steam blows the water out 
of the tube, and it overheats and burns. 

To prevent this trouble and insure circulation in water- 



TYPES OF BOILERS. 



465: 




Fig. 392. 



Fig. 393. 



w^^^''''>'>'y''^ri>i>;^rr^:w-)w^:;i4 /'■'/> '''-^'i^y 



• wj-rjMj"T^ '' /:"y-ju 




Fig. 393. 



4^6 MECHANICAL ENGINEERING OF POWER PLANTS. 



tubes which have to be of small diameter and essentially- 
vertical, the double tube has been used, sometimes called the 
Field tube. Within the water-tube is an open inner concentric 




Fig. 394. 

tube, reaching nearly to the bottom of the outer, closed tube, 
and held in place by fins or lugs. The diameter of this inner 
tube is so chosen as to leave an annular space all around 
between the two tubes, which is to be the channel for ascend- 



TYPES OF BOILERS. 



46; 



ing currents of steam-gas and hot water, while the central pas- 
sage within the inner tube shall carry the descending current 
of solid cooler water from above the outlet of the outer tube 




into the drum. It is expected also that the circulation and 
descent of the water in the inner tube shall be so rapid and 
vigorous as to wash out any sediment or scale from the bottom 



468 MECHANICAL ENGINEERING OF POWER PLANTS. 

of the outer tube where its presence would result in a burning 
of the tube. The circulation is active while the boiler is 
steaming, but it is not so when no steam is being withdrawn, 
and the circulation is that due to convection only. Under 
these conditions such tubes are apt to fill and solidify when 
least desired. Figs. 398 and 399 show the usual Field tube. 
It has been a favorite in fire-engine practice, and has also 
been used in tug-boat boilers. 




Fig. 397. 

Belonging also to the closed-tube class is a type with hori- 
zontal units projecting radially from a central vertical shell. 
The difficulties here are the cleansing of the inside of the 
units, and the indeterminate character of the circulation. It 
has been called the ** porcupine boiler." 

248 Bent- or Curved-tube Types. — To avoid the in- 
determinate circulation of the closed radial tube, it has been 
made an open tube by bending it back upon itself in an easy 
sweep, to enter the vertical water-drum at a different level. The 



TYPES OF BOILERS. 



469 



difference of level of the two ends is to maintain a determinate 
circulation while steaming, the bubbles rising and escaping at 





the upper end while water enters the lower end to supply 
their place. The tubes cannot be readily cleansed nor in- 
spected by eye except for a short distance. 



470 MECHANICAL ENGINEERING OF POWER PLANTS- 

This type of boiler leads to the class of water-tube boilers 
made up of bent tubes entirely, which will be discussed in a 
following chapter (pars. 261 to 263). Coil-boilers will be also 
there treated. 

249. Sundry Types of Externally-fired Boilers. — It is 
impossible within intelligent limits to present and treat all 
forms of boiler which have been proposed for special condi- 
tions or to meet the whim of particular designers or inventors. 
Such would be the types where sectional units of tubes have 
been placed in the gas-currents of an ordinary tubular boiler 
(Stead's), or at the sides of the fire-box and in the bridge- 
wall (Smith's); or the scheme of mechanical disengagement 
of steam by mounting the boiler on trunnions in its longitudi- 
nal axis, so that it might be slowly revolved over the fire 
(Pierce's); or the spray-boiler principle (Dunbar's), and many 
others no longer in use, or of questionable value or none when 
used. These belong rather to the specialist or expert field 
than to that of the practitioner, and when odd but successful 
types do come in that latter field they will usually prove to 
be combinations or new arrangements of standard types if 
they have desirable features in their design. 



CHAPTER XXII. 
TYPES OF BOILERS. INTERNALLY-FIRED SHELL BOILERS. 

250. Internally-fired Boilers. General. — The internally- 
fired boiler differs from the externally-fired boiler (par. 225) 
in that the fire in which the heat-energy is liberated is 
enclosed in a fire-box or furnace which forms part of the 
structure of the boiler and is surrounded on all sides (the bot- 
tom alone sometimes excepted) by the water to which that 
heat is to be transferred. 

The features of this principle are: 

(i) Economy. No heat is lost by radiation from brick- 
work external to the boiler and heated by the heat of the fire. 
The water to be evaporated intercepts all radiation. 

(2) The part of the boiler exposed so as to radiate heat to 
external air is no hotter than the water and steam within it. 
Loss by radiation is lessened here because of the lower tem- 
perature of the radiating body. This makes fire-rooms more 
comfortable, especially on board ship or in contracted quar- 
ters, and is of great importance in railway practice, where the 
boiler must be exposed to cool out-door air. 

(3) The metal surfaces surrounding the fire are most 
efficient evaporating surfaces. This makes such boilers com- 
pact with a given evaporative capacity, so that great evapora- 
tion is secured in a small space. This is of moment in 
locomotive and marine practice. Such boilers as are to be 
portable reap advantage from this. 

(4) The furnace being internal, the boiler requires either 
no setting or one of the simplest description. In wooden 
hulls the internal fire was a matter of great advantage in the 
matter of safety from fire, and the absence of a brick setting 

471 



472 MECHANICAL ENGINEERING OF POWER PLANTS. 

removes the difficulty from weight. The absence of setting 
makes such boilers portable, and fits them to be used where 
this is convenient. 

(5) They make steam quickly, so as to have pressure soon 
after starting the fires. 

(6) No cool air infiltrates through cracks or porous places 
in the brickwork to dilute the gases and lower their tempera- 
ture. Such infiltration may make a difference of ten per cent 
in efficiency in favor of internally-fired boilers which are self- 
contained. 

The objections to the internally-fired type are: 

(7) The internal fire-box exposed to a pressure tending to 
collapse it inward makes a costly type of boiler. This is 
offset in a comparison of types by the saving from the absence 
of setting. 

(8) The efficiency of the heating-surface keeps down the 
temperature of the gases, and thus prevents their complete 
combustion and causes smoky products of combustion. This 
is a real difficulty with coals containing much volatile matter, 
and vitiates economy of such boilers with such coals. Loco- 
motives and marine boilers are usually the worst offenders in 
smoky cities. The difficulty is increased when high rates of 
combustion are used. Means must be used to keep the gases 
hot enough to burn. 

(9) Rapid steaming capacity secured by large heating-sur- 
face, coupled with a small volume of water in the boiler at one 
time, makes a type in which pressure will rise rapidly from 
the safe working pressure to a pressure so much higher as to 
endanger the resistance of the shell to rupture. This makes 
such boilers dangerous in proportion to their liability to this 
trouble. 

(10) Many types introduce places in their structure which 
are hard to clean and inspect. 

(11) Circulation is not always perfect or satisfactory, and 
one part may have water in it which is much cooler than the 
average or normal temperature. This gives rise to unequal 
contractions and tends to develop leaks. Or the steam may 



TYPES OF BOILERS. 



473 



not be carried away from the heating-surface by the circula- 
tion, but may remain and keep water from touching and 
cooling the heating-surface, so that it becomes overheated. 
These do not attach to the same types, nor is either difficulty 
common to all types. The special features of any type will 
appear in their proper places. 

251. The Cornish and Lancashire Boiler. — ^The Cornish 
boiler is a single-flue boiler, with the fire-box or furnace at 
one end of it (Fig. 399). The flue is therefore of large 




Fig. 399. 

diameter (probably six tenths of that of the shell), and has to 
be stiffened against deformation and consequent collapse by the 
methods suggested in par. 232. The furnace is formed by 
inserting grate-bars supported on bearers across the flue, and 
its back is made by a brick bridge-wall. The gases pass back- 
ward through the flue to a back connection, whence they come 
forward either along the. sides or under the bottom if the 
chimney-duct is at the front; but if the chimney is at the 
back, the gases come to the front in side flues and return under 
the bottom. Such a boiler requires to be set in brick (Fig. 
402). 

The objection to the Cornish boiler is the large and weak 
flue. This early caused the development of the Lancashire 
boiler, which is sometimes called the double Cornish boiler. 
Two flues with internal fires replace the single flue of the 
Cornish. Each will be of smaller diameter and hence stronger, 
and the existence of two fires permits cleaning of fires and 
coaling to be done alternately in each, with advantage to the 



474 MECHANICAL ENGINEERING OF POWER PLANTS. 

steadiness of pressure. Fig. 400 shows a Lancashire boiler 
fitted with the Galloway water-tubes (par. 252). 




Fig. 400. 

A modification of this type in which two furnace-flues join 
into one flue behind their bridge-walls has been called in 
England the *' breeches " boiler. The American type of this 
has been seen in a form of locomotive boiler which the single 
flue serves as a combustion-chamber. The alternate-firing 
principle helps to keep up a high temperature in the combus- 
tion-chamber when one furnace is freshly fired with gaseous 
coal and the distilled products are ignited before getting into 
the fine subdivision caused by tubes (Fig. 401). 

252. The Galloway Boiler — The Cornish and Lancashire 
boilers are not usual in America, except in the modified form 
caused by introducing the Galloway tube (Figs. 400 and 402). 
This is a conical water-tube intended to cross the flue of either 
of the foregoing types, and serve both to stiffen it and to add 
a very efficient heating-surface of water-tube directly in the 
hottest current of the furnace-gases. The conical shape is 
given to the tube to favor circulation at uniform rate, but 
more especially to make it possible to pass the flange of the 



TYPES OF BOILERS. 



475 




47^ MECHANICAL ENGINEERING OF POWER PLANTS. 



smaller end of the tube through the hole made in the flue to 
pass the larger end, but not its flange. By this expedient 
one of the inner tubes which fails can be cut out and replaced 
by working from without the flue and without disturbing other 




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oooo 



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Fig. 403. 

tubes nearer the ends of the flue. The tubes may be alter- 
nately vertical and horizontal, or they may all diverge from the 
vertical. The flanges of the tubes serve to rivet them to the 
flue, one inside and the other outside (Fig. 402), and where 
the tubes brace the flue no stiffening-rings will be required. 



TYPES OF BOILERS. 



477 



The flue usually has provision for flexibility in case of unequal 
expansion of shell and flue (par. 232). 

253. The Scotch or Cylindrical Marine Boiler.— The 
cylindrical furnace arrangement of the internally-fired flue- 
boilers leads naturally to that form of boiler which is so 
generally used in the merchant marine. The large cylindrical 
shell will envelop or contain two or three internal flue-fur- 
naces, arranged as shown in Fig. 403 (see also Fig. 404). 
These furnace-flues being short are usually corrugated in 




ii 



FiG. 404. 



modern practice to give them stiffness against collapse without 
stiffening-rings. The flue is first welded lengthwise, and then 
corrugated i^ inches deep and with 6 inches between corruga- 
tions (Fig. 405). The end is flanged or straight to attach it 
to the front or rear sheets. Corrugation increases enormously 
the resistance to deformation by pressure, and its only draw- 
back is the difficulty in keeping it cleansed outside and in. 
At the rear of the furnace-flue the gases rise in a "back 



4/8 MECHANICAL ENGINEERING OF POWER PLANTS. 



connection" to the plane of the tubes, still surrounded by 
water, whereby the heat of the gases is more completely with- 
drawn; and from these tubes the gases and smoke pass into 
smoke-boxes and thus to the chimney-stack. Sometimes 
such boilers are made double-ended, either like Fig. 406, or 
with the back connection partly in common. The flat sur- 
faces of the back connection require careful staying as well 
as the large areas of the heads. The shells are butt-jointed 
and double- or manifold-riveted, by reason of the strength 
required with large diameters (par. 207). Such boilers usually 
have through-stays and stay-tubes as well. 

The Scotch boiler needs no setting and is self-contained. 
The objection to it is the tendency of the water below the 
furnace-flues to cool down and remain without circulation, 
thus preventing the shell from getting uniformly warm. This 




Fig. 384. 

is prevented in part by causing this lower water to circulate 
mechanically by means of connecting the suction of the feed- 
pump to the lower part of the boiler, while its delivery or 
forcing connection is toward the surface of the water in it. 
Other devices are also used for the same purpose. 



TYPES OF BOILERS. 



479 




--■-^ 







Li 



- I — ^ 




48o MECHANICAL ENGINEERING OF POWER PLANTS. 



The typical Scotch marine boiler is intended to be laid 
atiivvartship and to get a length of course for the gases by a 
return arrangement of tubes. This makes a large diameter nec- 
essary. For high pressure, and where the boiler can be laid 
lengthwise, the form of Fig. 407 gives the necessary length for 
the gases to give up their heat, and keeps the diameter down. 

254. The Rectangular Marine Boiler. Martin Boiler. 
— With the lower pressures used in the simple condensing 






IIII!iH||v 




III 






^^^i 






iliiiifiil 






1^9 






n 






i 







Fig. 408. 

engine rectangular fire-boxes or furnaces have been much 
used, and often the shell has been made with flat or arched 




Fig. 409. 
surfaces so as to fit the lines of the vessel to a degree. The 
gases may be led from the furnace by flue or tubes to the 



TYPES OF BOILERS. 



48 r 



back connection and then returned by flues or tubes to the 
front (Figs. 384 and 408). Sometimes the gases were returned 



III 




on a lower level (drop-return-tubular or flue boilers), and 
many combinations have been made of the tube and flue prin- 



4^2 MECHANICAL ENGINEERING OF POWER PLANTS. 

ciple. These boilers are sometimes called Martin boilers, 
although properly the Martin boiler had the return of the 
gases around nests of vertical water-tubes, crossing a rectang- 
ular return-flue. Such boilers had the trouble from inacces- 
sible central water-tubes in its worst form (Fig. 409). Flat- 
sided marine boilers are still to be seen for simple condensing 
engines in lake and river practice, but even here the furnaces 
are usually cylindrical and either corrugated or stiffened with 
rings (Fig. 410). Oil or grease settling from the water upon 
these furnace-crowns and causing them to soften and come 
down from overheating is a very frequent source of annoyance 
and danger in boilers of this class, and is aggravated by 
unwise handling of the engines. 

The conditions attending the use of the marine boiler in 
sea-going vessels call for a type of highest efificiency and best 
economy with least bulk and weight. The vessel must carry 
its own coal, and have to spare for any delay in reaching its 
next coaling station. Hence boilers of this class stand very 
high as types. Domes for such boilers are inconvenient, and 
for large diameters will either be dispensed with as not re- 
quired where a large steam space is furnished by the large 
diameter, or a dry-pipe will be used. For smooth-water boats 
the steam-chimney is still much used (par. 227 and Fig. 384). 

255. The Typical Locomotive Boiler. — The conditions 
imposed by the distance between the tracks of a railway line 
compel the boiler which furnishes steam to the locomotive 
engine to be of relatively small diameter, and hence of enor- 
mous heating-surface compared to the weight of water which 
it contains. The grate-area has been limited in early designs 
by the same conditions. Hence the rectangular fire-box has 
prevailed, and there has been no return-tube construction, 
but the tubes leave the front side of the fire-box. To get 
as wide a grate as possible between the driving-wheels, the 
water-legs were made narrow and parallel to the fire-box sheets, 
the two being stayed together by stay-bolts. The crown- 
sheet, of the same area as the grate, required to be very firmly 
stayed against collapse (par. 220 and Fig. 430) and steam-space 



TYPES OF BOILERS. 



483 



secured by enlarging the diameter over the fire-box, so that 
the name of ''wagon-top " boiler attached itself to this back 
part because of its resemblance to the canvas cover on hoops 
of the early plains wagons (Fig. 411). The fire-door is 




Fig. 411. 

formed in the back water-leg either by flanging the outer and 
inner sheets over each other and riveting them together, or 
else by means of a forged iron ring, whose width is that of 
the water-leg between plates, so that the two plates are 
riveted together with the ring between them. The inside 
dimension of the ring forms the size of the door. The 
bottom of the water-legs is either made of a similar ring — here 
called the "mud-ring" — or the inner plate is bent by a 
gentle reversed curve so as to come parallel to the outer plate 
and close to it, permitting the two to be riveted near the 
edge. Hand-holes give access to these water-legs, and a 
manhole must permit inspection of the crown-sheet. The 



484 MECHANICAL ENGINEERING OF POWER PLANTS. 




Mv| yfi 



TYPES OF BOILERS. 



485 






486 MECHANICAL ENGINEERING OF POWER PLANTS. 



tubes deliver the products of combustion into a smoke-box at 
the end farthest from the fire, from which the stack causes 
them to escape. On road engines the " extension-front '* 
smoke-box gives faciHties for catching and holding cinders. 
These are fitted below the outlet of the exhaust-pipes from the 
cylinders, so that no back pressure is created by sending the 
steam through spark-arresting appliances in the form of 
gauze or perforated sheets or both (Fig. 412). 

256. Modifications of the Locomotive Boiler. — The very 
excellence of the locomotive boiler for rapid and copious 




Fig. 430. 
steaming, its large heating-surface and strong draught when 
at work, are unfavorable to its economy and smokelessness* 



TYPES OF BOILERS. 



487 



Flaming gases are instantly put out on entering the tubes, and 
carbon is wasted and the unburned carbon in the gas appears 
as smoke. Combustion-chambers are therefore desirable, to 
give time and room for proper combustion, and they should 
keep the gases at high temperature, as well as admit of access 
of oxygen. Such combustion-chambers are secured by fire- 
brick arches across the ordinary fire-box, or by making special 
designs to secure them (Figs. 413, 414, and 430). The brick 
checkerwork is possible in stationary boilers, and becomes 
incandescent, so as to act both on the gases and by radiation 
upon the metal of the chamber. 

It is desirable, furthermore, while burning a given amount 
of coal, to lower the rate of combustion per square foot of 
grate-area. This can only be done by enlarging the area of 
the grate, lifting the boiler so as to be above the limit imposed 




Fig. 415. 

by the frames and by the driving-wheels at the fire-box end, 
and displacing the cab forward so that the fire-box shall be 
behind it (Figs. 414 and 415). Such wide fire-box will be fed 
through two doors, but its length will be fixed by the limit at 



MECHANICAL ENGINEERING OF POWER PLANTS. 



which coal can be conveniently thrown (usually eight feet^ 
possibly ten). Fig. 413 shows also a wide-grate design. 
Further modifications of the standard fire-box end have been 
hitherto presented (par. 220 and Figs. 331 and 432). Figs. 




THE MONARCH PORTABI E BOILER 

Fig. 416. 



416 and 417 show types which have been approved for sta- 
tionary practice and which favor economy while adhering quite 
closely to the locomotive class of boilers. 

Locomotive boilers have the advantages and disadvantages 



TYPES OF BOILERS. 



489 




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490 MECHANICAL ENGINEERING OF POWER PLANTS. 

of their class to a marked degree (par. 250). Besides their 
railroad use, they are used in high-speed torpedo-boats and 
over a wide field in stationary practice. 

257. The Upright Boiler. — The locomotive-boiler type 
becomes the upright type when the tubes are taken from the 
side of the fire-box and placed vertically in what was the 
crown-sheet of the horizontal boiler. Fig. 416 is a transition 




Fig. 417. 

type, and could almost be used in either position. The com- 
plicated staying of the crown-sheet disappears (Figs. 412 and 
430), and the fire-box and water-legs may conveniently now be 
made cylindrical, and the barrel part become of the same size 
as the fire-box part, or nearly so. Fig. 418 shows such a 
typical upright boiler, and Fig. 419 a modification of it. 
The fire-box is stay-bolted against deformation and collapse 
inward, and the water-leg is closed at the bottom with a 
mud-ring. Hand-holes give access to small places which can- 
not be visited. The tubes stay the opposite surfaces. 
The features of the upright boiler are: 



TYPES OF BOILERS. 



491 




Fig. 418. 



Fig. 419. 



492 MECHANICAL ENGINEERING OF POWER PLANTS, 

(i) It is light and portable. 

(2) It requires no setting. 

(3) It is a rapid steamer, because vertical tube-surfaces 
evaporate rapidly and the water is subdivided. 

(4) It takes little floor-space. 

(5) The upward motion of the hot gases is the natural flow 
of such gases. 

(6) The simplicity of the stays makes it a cheap boiler. 
On the other hand it may be urged : 

(7) The circulation is not determinate, and may be defec- 
tive. Everything tends to ascend all over, and if water does 
not replace the steam made at the tube-sheet, the latter will 
overheat. This is remedied in part by thinning out the tubes, 
so as to leave open spaces for water to move through, and by 
the use of baffle-plates or brattices to force a determinate 
circulation. 

(8) It is troublesome to get a dome or a large steam-space. 
Wet steam will result if the flow is rapid. 

(9) The upper ends of the tubes are not water-cooled in 
such a design as Fig. 418, but will grow very hot and expand 
so as to cause leaks at the upper tube-sheet. While such hot 
tubes may serve to dry the steam somewhat, the difficulty 
from unequal expansion is of sufficient moment to justify the 
design of Fig. 420, where the smoke-box is drawn down into 
the boiler proper to submerge or drown the ends of the tube 
below the water-line. 

(10) The boiler cannot be entered for a personal inspection, 
and cleansing is not easy when it has to be done from outside. 
This is a very serious objection with many waters. 

(i i) It holds the least amount of water of any of the shell 
types, which makes it pass quickly from safe pressure to one 
which would endanger it. This danger is greater the smaller 
the boiler. 

258. Modifications of the Upright Boiler. — To secure the 
convenience of the upright arrangement and at the same time 
avoid some of its defects, various special designs have been 
advanced. Fig. 4.21 shows the Corliss boiler, with a steam- 



TYPES OF BOILERS, 



493 




Fig. 420. 



494 MECHANICAL ENGINEERING OF POWER PLANTS. 




Fig. 421. 



TYPES OF BOILERS. 



495 



drum C arranged as a superheating surface, a mud-drum D to 
catch sediment, and an annular grate A, supplying the hot 
gases to the vertical tubes. The Reynolds boiler groups the 
tubes in such fashion that through a manhole full access is given 
between the rows to every part of the crown-sheet (Fig. 422). 




MM HOLE 



ggooooo^qooo \ 
-000000000000 



HAND HOLE 




HAND HOLE 



Fig. 422 

259. The Fire-engine Boiler. — The steam fire-engine 
boiler is a modification of the submerged-tube type of the 
upright, with the addition in the fire-box of extra heating- 
surface either in the form of Field tubes (par. 247) or of 
some of the curved water-tubes (Figs. 423 and 424). The 
fire-tubes are often of brass or copper to secure high conduc- 
tivity, and they are made of small diameter, and a great many 
are used very close together. Such boilers must have full 
working pressure in two or three minutes after the fire is 
lighted, and this property must be secured by having very 
little water in the boiler at one time. This makes a dangerous 
boiler in proportion to its ability to steam rapidly, and one 
liable to wide ranges of pressure in a short time. 



49^ MECHANICAL ENGINEERING OF POWER PLANTS. 




Fig. 423. 



TYPES OF BOILERS. 



497 




Fig. 424. 



GHAPTER XXIII. 

TYPES OF BOILERS. INTERNALLY-FIRED SECTIONAL 

BOILERS. 

260. General. — In a strict sense a sectional or water-tube 
boiler cannot be internally fired. But the demand for high 
pressures and a rapid steaming capacity in a small bulk, with 
the safety which results from the sectional principle, has 
caused the appearance of several types of boilers in which 
the fire is so completely surrounded by the water-tubes which 
form the heating-surfaces that it seems most fitting to group 
them in the class where this condition is a feature. These 
boilers furthermore have no setting such as is needed for the 
externally-fired sectional type, but the grate-fixtures attach to 
the heating-surface directly, and only a non-conducting casing 
is required to envelop them like a smoke-box and confine 
any products of combustion. While some forms of straight- 
tube boiler will lend themselves to the design of internal fur- 
naces of this sort, their use is not widespread as yet. Most 
of them are built up of curved pipes or tubes, the curvature 
being given in order to provide for expansion both equal and 
unequal, and the joints being made with fittings in smaller 
sizes, or by the method of expanding into special headers in 
the larger ones. 

261. The Water-tube Boiler. — Figs. 425 and 426 illus- 
trate the Almy boiler, a type of tube and fittings boiler which 
has been used with favor on high-speed yachts and torpedo- 
and dispatch-boats. The curvature of the water-tubes takes 
up expansions, and the fire is surrounded by the water to be 
evaporated. There is very little water in the boiler at one 

498 



TYPES OF BOILERS. 



499 



time, and it is thoroughly subdivided over a great heating- 
surface. 

Fig. 427 shows the Thornycroft boiler in two forms, and 
Pig. 428 the Ward, which has been a successful com'petitor 




Fig. 425. 

for recognition in larger marine practice. Their princioles 
have been so well canvassed already that further discussion is 
not called for. 

262. The Coil-boiler. — The coil-boiler differs from those 
above mentioned in that one or a limited number of continuous 



500 MECHANICAL ENGINEERING OF POWER PLANTS. 



coils is used instead of a large number of short or separate 
circuits. The steam formed near the bottom end of such a 
coil must run through its entire length before escaping at the 
disengaging-surface. This makes it desirable that the water 
in such a coil-boiler should be circulated mechanically, both 




Fig. 426. 

by reason of the advantage so far as efficiency of transfer is 
concerned, and to preserve the coil from burning. Such coil- 
boilers have given very large results for their size in experi- 
mental forms. The two best-known types are identified with 
the names of Herreshoff and Trowbridge (Fig. 429). (See 
also Fig. 424.) 



TYPES OF BOILERS, 




Fig. 427. 




4t4t4t4. 



II II II II II 



J J J J J 



^^ 



E^E 



. — -13S - — 

V /mO'S STEAM GENfl^A JOR 

Sue P 30 

As rested OrBo anf ^( J S. NaMlEnaineen 

Fig. 428- 



502 MECHANICAL ENGINEERING OF POWER PLANTS: 

263. Sundry Types. Conclusions. — As in the case of the 
externally-fired boilers, there will be types of internally-fired 
boilers which will not go naturally into the general classes 
above named. Such would be combinations of accepted types 
made for special uses, and possibly new types. The student 




Fig. 429. 

and reader must follow his own lead in the consideration of 
such cases. 

It seems to be held in the case of the water-tube marine 
boilers that they present the following features: 

(i) Light weight of both metal and water; about one half 
that of a Scotch boiler of equal steaming capacity. 

(2) Adapted for high pressures. 

(3) Make steam rapidly, and have the pressure soon after 
starting fires. 

(4) Are safe against a disastrous explosion, because they 
hold so little water. 

(5) Are not injured b.y the intense combustion and local 
heat caused when forced draught is used. 

(6) The parts are not difficult to renew. 
As disadvantages they offer: 

(7) They require more care in feeding. The water does 
not always remain in the lowest part of the coil and give a 
normal level at the water-gauges. When used in batteries 
the water may not remain in one particular boiler in mass, 
but will fly about in it or even into other boilers. 



TYPES OF BOILERS, 503 

(8) Corrosion is troublesome within the coils, and access 
and inspection impossible. Oil also gives trouble if allowed 
within the coil with the water. 

(9) The coil is prone to fail where the pipes or tubes are 
threaded into the fittings. Overheating from absence of water 
on the heating-surface makes the screw-threaded ends give 
out by oxidation and by stretching. 

(10) The casing around them gets very hot and makes the 
fire-room or stoke-hold hot even to the point of being un- 
bearable. 

(11) A certain greater amount of air is drawn into the fire 
around the casing so as to dilute the hot gases and lower 
their temperature. This does not occur in a true internally- 
fired boiler. 



CHAPTER XXIV. 

BOILER-SETTING. 

264. General. Side Walls. — The internally-fired boilers 
are ready to use as soon as they are located and properly sup- 
ported (the Cornish and Lancashire excepted). The exter- 
nally-fired boilers and these two examples of the former class 
require a structure to be erected which shall support them 
and shall provide a proper place for the fire and some of the 
flues or spaces for combustion. This structure is called the 
boiler-setting. It must be of a refractory material to with- 
stand heat, and of a non-conductor for heat so as to cause least 
losses by radiation. Its material must be easily manipulated 
to form flues of proper shape and character, and must be 
one with which it is cheap to build. 

These conditions are best met by the use of brick. Those 
parts exposed to fierce action of heat will be of fire-brick, and 
the rest of the cheaper common red brick. The fire-brick 
may be used as an inner lining on the fire-surfaces for the 
more massive walls, provided proper care be taken in bonding 
the two grades together. The fire-brick is a little larger than 
the common brick, which is an occasion for trouble in uniting 
them. Bridge-Walls and the thin parts at the front of fire- 
boxes will be of fire-brick altogether. Cheapness can be 
secured by using fire-brick only above the line of grate-bars 
both in the fire-box and behind it, but it is a question whether 
this is worth while. The fire-brick lining need not be carried 
very far into the chimney with anthracite fuels, since the gases 
should never be above 600° Fahr. after they leave a prop- 
erly set tubular boiler. With some sectional boilers the gases 
may be hotter, and with bituminous or long-flame fuels flam- 

504 



BOILER-SETTING. 505 

ing may occur within the chimney, making a fire-brick lining 
desirable all the way to the top. 

The thickness of the walls will depend in part on the 
methods used to support the boiler. If the setting of brick 
is to support the boiler and its contents, it must be at least a 
brick and one half thick (12 inches), and will be more usually 
17 or 20 inches for outside walls. The twenty-inch wall is 
usually made with a four-inch air-space between two eight- 
inch walls. This make a non-conducting wall for the sides, 
and with considerable stability, because at intervals a brick is 
laid headerwise across the air-space to tie the sides together, 
and at other intervals a header-brick in each wall is laid to 
project across and touch the other wall without entering it 
(Fig. 437). The hollow wall is without meaning in walls 
between the boilers in a battery. Such walls will be solid, 
and probably twelve inches thick. 

If the boiler is supported upon an iron framework inde- 
pendent of the brickwork as in the case of sectional boilers in 
the main (Fig. 385), the brickwork of the setting becomes a 
mere shell to retain the heat and gases, and may become an 
eight-inch solid wall or a twelve-inch wall with air-space. 

Rear walls which form a sort of reverberating surface 
require to be thick and well laid, because exposed to the 
deteriorating effect of heat in a marked degree. It is more 
usual to make these solid or without air-space, and depend 
for coolness upon the non-conducting quality of brick. 

The use of lime-mortar in boiler-settings is not to be com- 
mended. The heat tends to calcine the lime, or continually 
to unset or loosen the mortar bond, and the effect of hydrat- 
ing the calcined lime is to injure the iron which it may touch. 
Fire-clay mortar is refractory and harmless, and will be used 
in any case with the fire-brick work. 

265. Buck-stays and Tie-rods. — The heat of the fire and 
its gases causing expansion and deformation of the setting, to 
which the expansion of the boiler and its supports may add 
their influence, makes it necessary that the setting should be 
treated structurally like a heating-furnace, and tied together 



506 MECHANICAL ENGINEEKING OF rOWER PLANTS. 

by means other than the bond of the brickwork. For this 
purpose tie-rods will be laid lengthwise (Fig. 442) in side 




walls, and will be used also crosswise between the side walls. 
The lengthwise tie-rods bear at the front on the outer side of 



BOILER-SETTING. 



507 



the front castings, and at the rear either on buck-stays or large 
washers, against which they bear by means of a nut on the 
threaded ends of the rod. The side-wall ties bear on buck- 
staj^s (Fig. 437). 




Fig. 437. 
The buck-stay is a vertical bar of cast or wrougnt iron, of 
a section adapted to resist transverse bending. They are used 
in pairs on opposite sides of the setting, drawn together by the 
tie-rods and binding the section of the wall against which they 
bear. Usually there are three pairs in the ordinary length of 
a boiler-setting. Their section may be a T iron, with the flat 
of the head against the wall (Fig. 442), or any convenient 
structural section may be used. Old rails used in pairs will 
bemetduite often. Tje-rods need not be used at the bottom 



5o8 MECHANICAL ENGINEERING OF POWER PLANTS, 

of the setting, provided the feet of the buck-stays be let 
securely into the footings upon which the walls are built (Fig. 

459)- 

266. Hanging of Boilers. — The weight of a shell or sec- 
tional boiler is considerable, and when its contents of water 
are added, the method of carrying this weight requires to be 
carefully studied. 

Two methods are usual. The boiler is supported at its 
sides at about the horizontal diameter, or it is hung from 
above by eyes and links attached to its upper part, and sym- 
metrical to a vertical diameter. 

The first plan calls for projecting brackets or ''lugs " to 
be riveted to the shell along its sides, and giving strength 
sufficient to carry the weight. These lugs will be of cast iron 
or steel castings, either solid or with the projecting part fitted 
to slide home in a socket made for it and fastened to the shell. 
The number of these lugs will be fixed by the length of the 
boiler. Two on a side is best if possible, since then every lug 
carries not far from one fourth of the load, no matter how the 
boiler may be deformed by expansion. If there are three 
or more lugs on a side, then when the lower elements of the 
boiler lengthen, the end lugs lift, and most of the weight is 
on the central pair; if the lower elements shorten relatively, 
then the boiler lifts off the central pair and is carried at the 
ends. These changes in length come from impact of cold 
feed-water, or of cold air when the fire-doors are opened wide 
and suddenly. Figs. 436, 375, 441, and others show such 
lugs and their forms. 

The other method of support calls for an eye on the top 
of the boiler (Fig. 321), or on the two sides (Fig. 438), into 
which a hooked link may be fitted, so as to hang the boiler to 
a pair of cross-beams of structural material, the latter carried 
either upon the side walls as abutments, or by metal columns 
independent of the side walls. Sectional boilers may be hung 
from the top, from the sides, or from the bottom, as may be 
most convenient and preferred. 

The method of support by lugs usually depends upon the 



BOILER-SE TTING. 



509 



side walls to carry the weight. To prevent injury to the 
walls, the wall is fitted with plates under the lugs to distribute 
the load, and to furnish a surface for the motion of rollers of 
half-inch round iron inserted between the plate and the lug- 
surfaces at one end so as to allow a free end to move length- 
wise in expanding and contracting without pushing the wall 
or deforming the shell (Fig. 457). The rollers may be omitted 




Fig. 438. 

in light boilers, and the boiler allowed to slide on the plate. 
This pushes the wall about, however. The end to be fixed 
is determined by the convenience of the attachments to the 
boiler. The locomotive boiler is fixed at the front to the 
cylinders and frames, and is free to move at the fire-box end ; 
most stationary boilers are fixed at the furnace end and ex- 
pand toward the rear. 

Expansion in suspended boilers is provided for by the sus- 
pending link, and by this their expansion is independent of 
the brickwork. This is the great advantage of this method 
of hanging. The objection to it Avith large-diameter shell 
boilers is that the weight tends to make the flexible shell 
take an oval shape when pressure is low, while the internal 
pressure restores the cylindrical shape when it rises again. 
The flexure of the longitudinal joints caused by these changes 
of shape causes grooving near the joints, to be discussed in 



510 MECHANICAL ENGINEERING OE POWER PLANTS. 



pars. 338 to 343. With shells of small diameter this trouble 
is scarcely felt. 

With very long cylindrical boilers the necessity for many 
points of support conflicts with the considerable changes of 
shape by heat in such long lengths. This has given rise to 
the method of hanging by means of equalizing-levers over the 
transverse supporting beams (see Fig. 372), whereby each eye 
carries its proportion of load in every condition of shape; or 
the same result is approximated by using stiff spiral springs 
(like car-springs) under the nut on the suspending links which 
hook into the eyes. When the boiler curves itself length- 
wise, the spring accommodates the excess or relief of load, 
without causing so much strain on the plates of the boiler 
itself. A skilful designer, compelled to use long boilers, has 
cut them into lengths and linked them together by flexible 



R R R R R 


Y Y (C\ Y Y 


C ZXL itiz Z\ 



Fig. 439- 

connections of copper tube (Fig. 439), in ordei to meet 
this serious trouble. 

267. Boiler-fronts. — It would be possible to make the 
front part of a boiler-setting of brick, but it is not usual to do 
so, because the openings through it for access to the furnace 
and ash-pit, and to the boiler itself, would make troublesome 
and short-lived constructions in brick, and would make the 
door-fittings difificult. Hence the use of cast-iron fronts for 
settings is universal, for their convenience and cheapness, for 
ease of fitting, and for the effect to the eye which as completed 
structures the boiler-settings can be made to produce. They 
will be made in one or two sections set up edgewise, and held 
in place by the nuts on the ends of the longitudinal tie-rods 
through the walls (par. 265). 



B OILER-SE T TING. 5 I ^ 

Boiler-fronts are either full fronts or half fronts. The full 
fronts are sometimes called flush fronts, and the half fronts are 
also called extension or overhanging fronts. The full or flush 
front will be used always with sectional boilers, usually with 
tubular boilers, in which the products of combustion are to be 
carried backwards over the top of the shell to a chimney 
behind the boiler, and quite often where the gases are to be 
taken from the front end of the boiler to a chimney by means 
of a sheet-iron duct. When the full front is used the side walls 
will be carried up level with the top of the front (Fig. 436), 
and the joint between the side walls over the boiler will in 
this case be made either arching, or by means of filling in on 
top of the boiler with some non-conducting material. 

The half fronts will be used where the side walls are to be 
carried up to the height of the supporting lugs only, and the 
smoke-box is to be made an integral part of the boiler itself 
(Figs. 442 and 459). A cylinder of a relatively light boiler- 
plate is secured to the shell of the boiler itself and, projecting 
beyond the plane of the front, forms a smoke-box indepen- 
dently of it. This arrangement is shown in Fig. 442. It 
implies of necessity that the gases are to be taken off from 
the smoke-box either directly to a chimney-stack or by means 
of a sheet-metal flue or breeching. 

There will be three sets of openings to be made in the 
boiler-front, each of which must be closed by proper doors. 
In the full or flush front these three openings are all made in 
the front proper. In the half front the two lower ones will be 
formed in the front, and the upper will be a part of the struc- 
ture of the extension smoke-box. The top of the front is 
then curved to match the curvature of the shell or smoke-box 
which protrudes beyond it (Fig. 443). The lowest opening 
gives access to the space below the grates, which is called the 
ash-pit. The doors which close it are called the ash-pit 
doors. These doors are a means of controlling the draft of 
air which passes up through the fire, and will be closed when 
the fire is to be checked. From examination of Figs. 436 
to 445 it will appear that such doors may be either a single 



512 MECHANICAL ENGINEERING OF POWER PLANTS. 

large door, two smaller doors closing a large opening, or two 
independent openings each with its own door. The advantage 
of small doors is the diminished strain on the hinges when 
such doors are opened, and the fact that such short doors are 
less in the way than long ones. It is not unusual to make 




Fig. 440. 

register-openings in these doors, but they have comparatively 
small significance since it is much easier to leave the door 
slightly open if but a little air is desired. 

The second set of doors open into the furnace or fire-box 
on a level above the grates, and each will be called a fire-door. 



BOILER-SETTING. 5 1 3 

Its function is to give access to the fire for charging it with 
fuel and for cleaning, and it also has a use in the control of 
the fire, since by leaving it open cold air from the fire-room 
enters above the fire, lowering the temperature of the hot gases 
by dilution and actually serving to cool the boiler, while at the 
same time the easy passage of air over the fire checks the draft 
through it. The same considerations as to the use of one large 
or two smaller doors are to be noted with respect to the fire- 
door, but the latter requires that it should give access for 
coaling and cleaning to every part of the grates, and conse- 
quently with a wide furnace two doors become a necessity. 
They have the further advantage that in coaling and cleaning 
they need not both be open at once. The single door is 
better than two doors which overlap, when it is possible to use 
it, because it closes the fire-opening somewhat more tightly. 
The minimum width of a fire-door should permit the easy 
handling of an average coal-scoop, which measures for small 
coal 14 inches across. 

The fire-door furthermore requires a special construction 
to prevent its becoming unduly hot by radiating heat from the 
fire. This is done by forming an air-space between the outer 
surface, which is the door proper, and the inner plate of per- 
forated iron which is fastened to the door with distance-pieces 
to keep them at a fixed distance apart (Figs. 440 and 441). 
The inner or baffle plate receives the heat of the fire, and the 
circulating air between the baffle-plate and the door serves to 
carry off some of the heat. The fire-door is often also made 
with register-openings to permit a certain amount of air to 
enter this air-space and so reach the fire above the grates. It 
is difficult to provide sufficient area to make these openings 
serviceable to supply oxygen for combustion, but the old rule 
used to be that such openings should be 2 square inches for 
each square foot of grate-surface with short-flame fuels, and 
5 square inches where the fuel contained much volatile matter. 
The real use of air above the fire can be best obtained by 
leaving the door slightly open when it is required. 

The third set of doors will be called in shell boilers the flue- 



514 MECHANICAL ENGINEERING OF POWER PLANTS. 

doors, and are intended to give access to the front of the 
boiler for cleansing the i^ues or tubes and for inspection. 
In full fronts and with boilers of large width it is desirable to 
make these doors double in order to keep their weight down 




Fig. 441. 



They will then be arranged to open on vertical hinges, and 
Avill be held shut by a common latch. In extension fronts it 
becomes more convenient to make the opening to the smoke- 
box for inspection by a door turning upon a horizontal hinge 
at about the horizontal diameter. Figs. 436 to 447 and 



B OILER-SE 7 ' TING. 



SI5 




5l6 MECHANICAL ENGINEERING OF POWER PLANTS. 



Fig. 451 show typical constructions covering these points 
and methods. 

Fig. 433 illustrates a type of extended front which has 
received some approval among the pure-water conditions in 




Fig. 433 
New England. The front of the furnace is a water-leg, 
through which the fire-door is made. It would be improved 
by provisions to secure a determinate circulation of the water. 
Cleansing is effected bv the two blow-off pipes (par. 324). 

268. The Dead-plate and Mouthpiece of the Furnace. 
— When the smoke-box or front connection is formed behind 
the cast-iron front, the boiler will stand behind that front a 
distance which is the depth of that smoke-box (Fig. 436). 
The front end of the gyrate-bars should not project beyond the 
end of the heating-surface of the boiler, and therefore a dis- 
tance equal to the depth of the smoke-box will lie behind the 
fire-door and between it and the end of the bars. This sup- 



BOILER-SE TTING. 



517 



plies furthermore a space such as is required in a method of 
firing which is called the coking method of firing, which has 
given rise to the name of dead-plate to the solid cast-iron 
plate which forms the bottom of the furnace mouthpiece. 
The coking method of firing is to charge the bituminous coal 




Fig. 443. 

upon this dead-plate and not upon the grate-surface proper. 
The heat from the burning fuel on the grates distils off the 
gas and all volatile matter which passes backwards over the 
fire; but since there was no openings in the dead-plate, 
oxygen does not come up through the fresh coal to set fire to 



5l8 MECHANICAL ENGINEERING OF POWER PLANTS. 

it. When distillation has proceeded far enough, and the coal 
is partly made into coke upon the dead-plate, it is then pushed 
back upon the grate-area and burned as hard coal would be 
burned. Even with anthracite firing, where no coking is re- 
quired, the dead-plate remains as a distance-piece, but with- 
out significance or use in firing. It usually forms the top of 
the opening into the ash-pit below, and is simply a plate of 
cast iron built into the brickwork of the setting at the sides 
(Fig. 443). In some cases the dead-plate has been made to 
drop by hinging the front end against the boiler-front and 
holding up the back by a latch which can be released. The 
object of this arrangement was to permit clinker and ashes 
too large to pass through the grates into the ash-pit to be 
dumped into the latter over the ends of the bars without 
coming out through the fire-door and causing unpleasant 
odors from any cause which such material might give off in 
the open fire-room. 

The sides and top of the furnace-moutn opening will be 
made either of cast iron, like the dead-plate which forms its 
bottom, or of fire-brick. The latter may be either the ordinary 
forms of fire-brick, or specially moulded shapes can be obtained 
whereby the mouthpiece has but a few joints in it to give 
trouble in service. The mouthpiece must flare towards the 
furnace in order that an opening smaller than the width of the 
grates may permit access to every part of the grate, and the 
injury from firing-tools and from the action of the heat of the 
fire makes trouble with ordinary brick construction. The arch 
over the door is also a flat one which it is troublesome to 
make and maintain if of many separate pieces. The sides 
are sometimes of the usual sizes of brick, and the top of cast 
iron. 

269. The Ash-pit. — The ash-pit, as its name indicates, is 
to catch the refuse incombustible matter when the fires are 
cleansed. It is simply formed by the sides which form the 
furnace, and is paved on its bottom with fire-brick also. The 
bottom is sometimes made lower than the general floor-level 
(Fig. 444) in order that water may be allowed to lie in the 



B OILER-SE T TING. 



519 



depression thus formed. The object of the water is first to 
quench incandescent matter which if allowed to glow in the 
ash-pit would heat and soften the grate-bars. It is desirable 
also that if sulphur-gases are given off from such ash, the 
process should be stopped at once. It is further urged that 
the steam formed from this water will tend to keep the grate- 
bars cool on its passage through them, and the combustion of 
the hydrogen, when such steam is dissociated in the fire, will 
add to the heat of the usual combustion. The objection to 




Fig. 444. 

this is that the dissociation of the steam cools the fire itself 
exactly to the same extent that the combustion of hydrogen 
would raise its temperature. With short-flame fuel the hy- 
drogen may act to lengthen the flame and increase the effect 
of radiation in a perceptible degree. With long-flame fuel its 
effect is not observable. It is a question whether steam from 
the ash-pit may not act to rust metallic surfaces and to form 
a more active compound with the sulphur-gas given off thaa 
when that gas is dry. 

When the air for combustion is to be supplied to the fire 
by mechanical means so as to create an artificial draught by 
pressure below the grates, the flues or ducts for such artificial 



520 MECHANICAL ENGINEERING OF POWER PLANTS. 

draught will be carried into the ash-pit. The best places are 
the side walls, rather than the bottom, since it is difficult 
to keep ' ashes from dropping into the ducts when the open- 
ings are directly under the grates. These openings will be 
controlled with proper dampers operated from outside of the 
setting. 

In large plants where the weight of ashes to be disposed 
of in any day becomes very large, it is worth while to arrange 
the ash-pits so as to deliver their accumulations into a tunnel 
underneath them through which convenient wagons may be 
wheeled to receive the contents of each pit as it stands under 
a convenient opening below it. This principle also becomes 
of importance when the mechanical methods of firing are 
used whereby the grate is made to be self-cleansing and dis- 
charges its ash and incombustible matter continuously over 
its end. If the wagon method is inconvenient, it may be 
replaced by a continuous conveyor whereby the discharge from 
each grate or ash-pit falls upon a continuously moving band, 
and is carried by it and dumped into some convenient recep- 
tacle outside. 

270. The Furnace. — The furnace of the boiler forms the 
very central feature of a successful and economical power 
plant, because it is there that the energy resident in the fuel 
is liberated and transformed from potential to actual energy. 
The chemical reactions between carbon, hydrogen, and oxygen 
are the means for the liberation of this energy, and the sub- 
ject is so important that the boiler-furnace may properly claim 
a later chapter for itself. The subject further must embrace 
the questions of economy and efficiency consequent upon the 
rapidity or intensity of these chemical reactions, and the sub- 
jects of the absorption of the liberated heat by the water and 
its transfer to the metal of heating-surface, belong also to the 
same category. The design of the furnace with respect to the 
fuel to be used in it is also a matter of primary importance, 
whether solid, liquid, or gaseous, and, if solid, whether wood 
or coal is to be used and in what forms; mechanical stoking, 
smoke-prevention, and similar questions attach to it. For the 



BOILER-SETTING. 521 

present purpose in its relation to the boiler-setting certain 
practical details only will be considered. 

271. The Grate-bars. Stationary Grates.— In a boiler- 
furnace to be ised with a solid fuel sucn as coal, the fuel 
must be supported in sucn a manner that the necessary oxygen 
for combustion can be brought into contact with the caroon 
of the fuel by passing up through the body on which it lies. 
This demands that the grate-surface shall be so constructed 
that coal shall not fall through the noles left for the passage of 
air. In general the problem has been met by making the 
grate of bars, either of cast iron or of wrought iron, solid or 
hollow. Grate-bars may be divided into three classes: the 
fixed or stationary grates, shaking and dumping grates, and 
mechanical or travelling grates. 

The stationary or fixed grates are almost always of cast- 
iron bars (Fig. 447). It is most usual to run these bars length- 
wise or in the direction of the axis of the boiler ana perpen- 
dicular to the front. It is easier to clean them when arranged 
this way. They will be supported by transverse bars, usually 
of wrought iron, let into the brickwork of the side walls. 
There is usually one at the front and one at the back support- 
ing the bars at their ends. It may be, however, that instead 
of running the bar continuously the whole depth of the fur- 
nace, it will be divided in the middle, and each short bar will 
rest upon a third bearer midway between the other two (Fig. 
445). The conditions which a cast-iron grate-bar must fulfil 
are as follows: 

(i) The bar must be cheap to make by casting in the open 
sand of the foundry. 

(2) It must give adequate support to the coal on it, and 
yet must permit the access of air through it from below. 
This air is depended on to keep the bar cool, as well as to 
furnish the oxygen for combustion. 

(3) The bar must be of such design that it shall not warp 
under the unequal temperature of its upper and lower sides. 
Warping rnust be prevented both vertically and sidewise. 

(4) The bar must be easily cleaned from ashes and clinker, 



522 MECHANICAL ENGINEERING OF POWER PLANTS. 



and yet must not be so fragile as to break under the ordinary 
treatment with the fire-tools. This convenience of cleaning is 
usually secured by giving the bar a section like a wedge with 




Fig. 445. 
the broad back up. Any solid matter which will pass through 
the top opening will go the rest of the way and fall into the pit. 
(5) The bar must be strong enough to carry the load caused 
by the weight of fuel without sagging or breaking even when 
its top is red-hot. This is secured by giving considerable 
depth vertically to the bar, so that the bottom side of it, which 
is met by the incoming cold air, shall be quite a distance away 
from the hot surface of the top, which would warm it by con> 
duction. 



BOILER-SETTING. 



523 



(6) The bar must not be so heavy that the handling of it 
becomes difficult in the contracted quarters in which it is to 
be placed. 

It would appear that a maximum relation between the 
supporting function of the bar and free passage of air would 
be reached when each was made 50 per cent of the surface of 
the grate. Practically this relation cannot be reached without 
causing much unburned fuel to fall into the ash-pit to be 
wasted, or to entail the labor of picking over if it is to be 
saved. The difficulty is worse as the size of the fuel grows 
smaller. It is usual to consider the bar satisfactory for the 
passage of air when 25 per cent of air-space is presented by 
its design. The proportion of 
air-space to solid surface of the 
bar is usually determined by the 
expedient of laying the bar upon 
a piece of stiff paper, tracing its 
profiles of openings with a sharp 
pencil, cutting out the paper 
representing the openings, and 
weighing on delicate scales the 
relation of the weight of the air- 
space and solid bar in any given 
unit of area. 

The usual deterioration and 
failure of grate-bars comes from 
their warping, from fusion of the 
top surface, and consequent softening and loss of strength, 
and from breaking through by their own deterioration or 
from a deterioration caused by the continued heat. 

Wrought-iron bars when made solid are particularly 
troublesome from a tendency to warp and to bend from soft- 
ening by heat. Wrought iron is less stiff than cast iron. 

When for any reason the air which enters under the grates 
is to be preheated so as to lose its cooling effect, solid grate- 
bars of either cast or wrought iron give trouble by their soften- 
ing. For this condition and in certain other places hollow 




Fig. 446. 



524 MECHANICAL ENGINEERING OF POWER PLANTS, 

wrought-iron grate-bars are used through which the feed- 
water or the water from the boiler is caused to circulate. 
This is to keep them from reaching the temperature of soften- 




ing, and adds to the heating-surface of the boiler. The diffi- 
culties from the expansion of such water-grates make them 
troublesome to join to the ends, but they have formed a satis- 
factory solution for many problems, and are a necessity in 



BOILER-SETTING. 



52s 



what is called the down-draft furnace, to be referred to here- 
after. Some of the bars in locomotive-boilers are usually 
water-tubes. 

With very fine fuel, such as coal-dust, and where sawdust 
is used as fuel, the grate-bar has to become a perforated plate. 
Where oil or gas is used the grate-bar disappears entirely, and 
the gas will be passed up through the perforations made in a 
fire-brick or similar floor which converts the grate into a form 
of burner. 

272, Shaking and Dumping Grate-bars. — The stationary 
or fixed grate-bar is cleaned by running a proper tool, called 
a slice-bar, over the top surface, or a poker between the bars. 




Fig. 448. 

This is a labor of considerable difficulty and requires that the 
furnace-door should be open while it is going on, and the cold 
air thus admitted not only deadens the fire but cools the 
heating-surface and checks the generation of steam. What 
are called shaking-grates are grates whose bars are so con- 
structed that by a lever or similar means a motion can be 
given to the bars, from without the setting, whereby the fire 
shall be agitated, the fine dust or ashes shall be shaken down- 
wards through the openings of the bars, and the ash or clinker 



526 MECHANICAL ENGINEERING OE FOIVEK PLANTS. 

which has attached itself to the top surface of the bars shall 
be broken up and ground into pieces fine enough to drop 
through and leave the fire clean. This result is attained in 
various designs of grate -bars by different mechanical methods. 
In some the bars are supported by proper bearers at their 
ends, to which bearers such a motion is given that the alter- 
nate bars move lengthwise in opposite directions through 
several inches of travel when the lever of the shaking mechan- 
ism is worked (Fig. 448). In others each individual bar re- 
ceives a rocking motion around the axis upon which it is sup- 
ported. The rocking motion lifts the fire and lowers it, thus 
shaking out the accumulation of ashes and dirt. 

Dumping-grates are a form of shaking-grate in which the 
motion which shakes the bars when carried farther opens suffi- 
cient space between the adjacent bars to allow the fire to slip 
off the top surface of the bar into the space thus opened and 




Fig. 449. 

fall into the ash-pit below. The difficulty with the dumping 
type of grate-bar is that carelessness in its use causes a loss of 
an excess of fuel in cleaning (Fig. 449). 



1 



BOILER-SETTING. 5^7 

The advantages of the shaking-grate are as follows: 

(i) The fire-door is opened for coaling, but not for clean- 
ing. 

(2) The fire-box lasts longer, because not exposed to the 
shrinkage and deterioration caused by cold air coming in upon 
its heated surface. 

(2) The firing is more regular, because the fires are kept in 
a condition of good efficiency by being always clean, and are 
not torn to pieces by the effort of the fireman to cleanse them. 
This is particularly true with anthracite as a fuel. One man 
can attend to more furnaces when the labor of attending to 
each is so much lightened. 

(4) The duty of the fireman is made less arduous and 
exhausting when he does not have to face the intense heat of 
the furnaces at the open doors for so long a time. 

The objections to the shaking-gate are as follows: 

(i) It does not work with all varieties of bituminous fuel. 
Where the coal is what is called fat, so that it fuses together 
on the upper surface of the fire, the shaking-grate does not 
cleanse the fire, but only leaves a hollow space below the real 
body of the fire. For coal of this class the use of the slice- 
bar is necessary in any case, and it might as well be used 
altogether. 

(2) The trouble and annoyance from machinery of any 
sort in an ash-pit. It cannot be lubricated; it is exposed to 
grit and dust. 

(3) The efficiency of the bar for cleansing usually throws 
down excess of unburned fuel into the ash-pit. The shaking- 
grate for stationary practice is usually considered to be a 
stepping-stone on the way to the use of mechanical stoking, 
and its advantages are usually reaped with the advantages 
which the latter offers. 

273. Step-grates. ^ — For the burning of fine coal, and par- 
ticularly in soft varieties where a large quantity of air is a 
necessity, a form of grate has been long used which is called 
the step-grate. The bars are flat surfaces or treads arranged 
so that the upper one slightly overlaps the one below it, while 



528 MECHANICAL ENGINEERING OF POWER PLANTS. 




BOILER-SETTING. S^9 

leaving the space open which corresponds to the riser in stair- 
way construction for the passage of air. It will be seen that 
this construction permits abundance of access of air with little 
or no possibility of coal dropping through the grate-surface. 
When the bars are laid across the furnace, as is usual, the 
slice-bar of the fireman can cleanse each bar separately by 
working through the vertical opening between the bars, or the 
method of firing may be used whereby the coal is fed first on 
the upper bar, and from that is gradually pushed down the 
steps from bar to bar until at the bottom it will be pushed off 
with all available combustible matter utilized, and only refuse 
and ash remaining. 

It is very easy to make such a step-grate become a shak- 
ing, or dumping-grate by arranging each bar so as to permit a 
motion to tip it down the steps. This can be done either by 
hand or by mechanical means (Fig. 450). 

274. Mechanical or Travelling Grates. — The principle of 
successive passage of fuel from bar to bar suggested in the 
previous paragraph leads to a construction of grate which is 
known as the travelling-grate. The bars, instead of being 
continuous and solid, are made up of a series of short bars 
which are pinned together so as to form a flat chain with the 
links edgewise. Chains of these flat links, made endless, 
mounted upon proper carrying-rollers at the front of the fur- 
nace and at the rear, and having the width of the furnace- 
area, can be driven by machinery attached to the rollers so 
as to draw the chain from the front of the furnace to the back, 
carrying on its surface the fuel to be burned. The speed of 
driving should be so proportioned that the fresh fuel charged 
at the front upon the travelling bed of the grate should be 
completely burned during the period of its transition to the 
back, so that when a given series of links reaches the rear 
roller and is dropped over, there is carried with it and dropped 
only the incombustible matter in that given amount of coal. 
Such a grate is practically self-cleansing and leads at once to 
the use of an automatic appliance for feeding the fuel to it to 
make it complete. Fig. 45 i will show a typical travelling- 



530 MECHANICAL ENGINEERING OF POWER PLANTS. 

grate, and Fig. 454 a type of grate in which the passage of 
fuel from step to step is made to be automatic by mechanical 



MECHANISM OF COXE'S CHAIN GRATE STOKER 




Fig. 451. 

means. It will be seen that the mechanical grates of this type 
lend themselves and lead naturally to the principle of the 
automatic stokers 

275. Mechanical Stokers.— If the self-cleansing grate can 
be combined with automatic feeding by mechanical means 
of the fuel which is to be burnea upon the grate, it will be 
apparent that not only has the supply of fuel as a source of 
energy become uniform and continuous, but the combustion of 
the fuel is made also regular and continuous because the fire 
is at all times in the same condition. Furthermore, the labor 
ot the fireman has changed from a hard muscular exertion of 
hand firing to the skilled supervision of machinery of sufficient 
power to do the required work. In the mechanical stokers 
which have been approved the coal is fed uoon the travelling 
or mechanically moving grate from a hopper, either through 
an opening or between rolls which carry ribs lengthwise so as 
to form pockets to receive the fuel, whereby the speed of 
these pockets measures the quantity of fuel delivered (Fig. 
360). The travelling-grate or the measuring-rollers can have 
their speed regulated by simple mechanical means connected 




BOILER-SE T TING. 



531 



with the steam-pressure; and if the air for combustion is sup- 
plied by mechanical means, the volume of that air can be reg- 




ulated by the rise and fall of the pressure of steam by causing 
the latter to vary the speed of the engine which drives the fan 
or controls the valve which supplies the steam-jet Fig. 452 



532 MECHANICAL ENGINEERING OF POWER PLANTS. 



shows a form of automatic stoker embodying some or all of 
these features, and Fig. 453 another type in which the motion 







Fig. 453. 

of the step-bar itself causes the fuel to be carried down the 
steps to be delivered as ash at the bottom. It will be seen 
that the form of grate shown in Fig. 450 can also be very 
easily and properly fitted to the principle of automatic stok- 
ing. The supply of fuel to the hoppers at the boiler-fronts 
will be done by the principle of mechanical conveyors with 
elevators if the supply of coal in pockets cannot conveniently 
be made overhead. If the coal-vault can be over the boiler- 



BOILER-SE Tl ING. 



533 



^W. ' ==.=■= 




534 MECHANICAL ENGINEERING OF POWER PLANTS, 







BOILER-SETTING. 535 

room, the coal may descend by gravity through proper spouts 
into the furnace-hopper without handling. 

This principle of mechanical handling of fuel, combined 
with mechanical handling of ashes (par. 269) and with the 
principle of automatic control of the machinery of stoking as 
the steam-pressure may vary, gives to a modern power plant 
where the principle is applied all advantages derivable from 
doing away with human labor and replacing it with intelligent 
control of inanimate force. It has not been proved that the 
advantages from uniformity and continuous action represent 
everywhere a surplus sufficient to pay for the increased cost 
of the installation, but the saving of labor expense leaves a 
margin, in a plant of any considerable size, which is abundant 
to offset such cost. 

Mechanical stoking has not achieved its best success with 
the hard varieties of anthracite coal with which the fireman's 
labor is the least. With certain varieties of bituminous coal 
which cake and melt it has been found that their working is 
not satisfactory in every case. Fig. 455 shows a form of 
stoker in which the feeding of fresh fuel is done from the 
bottom, so that the products of the first distillation are forced 
to pass up through the bed of incandescent fuel from which 
the gases have been removed. This brings them up to the 
point of ignition, and the slope of the sides of the bed of fuel 
is covered with coal in the condition of fixed carbon, which 
when completely burned falls off as clinker or ash at the sides 
of the grate, or is removed by slicing. 

276. Inclined and Horizontal Grates. — It will be noticed 
by examining Figs. 456 and 457 that a difference of prac- 
tice prevails with respect to arranging the grate-bars hori- 
zontally, or inclining them backwards at the back in the pro- 
portion of about 3 inches in 6 feet. The practice of inclining 
is quite usual, in order that the under surface of the fire may 
come more nearly normal to the incoming air-currents, so as 
to invite them to pass equally through all parts of the fire, 
rather than to take the easiest course. In sectional boilers 
with inclined water-tubes the inclined grate is of advantage in 



53^ MECHANICAL ENGINEERING OF POWER PLANTS. 

keeping the surface of the radiating fire more nearly parallel 
to the absorbing surface of the tubes. Inclined grates are also 
easier to clean by slicing. 




The horizontal grate renders it more easy to keep the fire 
of even thickness at the front and back, and makes it slightly 
easier to withdraw the clinker and other solid matter which is 
to be drawn forward and out through the fire-door m arrange- 



B OILER-SE T TING. 



537 



ments of this sort. The general prevalence of the 'inclined 
bar seems to indicate that it offers advantages over the other 
arrangement. 




Fig. 457- 
The level of the grate-bars with hand-firing should be so 
selected as to make the cleaning and coaling convenient to the 
fireman. This seems to be secured by having the top of the 
grates about 30 inches above the general floor-level. The 
depth of the furnace or the length of the bar with hand-firing 
seems to be determined by the twofold considerations of ease 
of cleaning and the satisfactory spreading of fuel. When the 
fireman stands on the floor-level he can easily deliver coal 
with precision at the back of the grate, which is 6 or even 7 
feet deep. When he stands above the grates, as in the case 
of the locomotive, he can throw coal to the back of a fire-box 
10 feet deep. Cleaning however, by hand, cannot easily be 
done with a furnace deeper than 6 feet, and this is usually 



538 MECHANICAL ENGINEERING OF POWER PLANTS. 

placed for the limit of the length of the grate-bar. With 
shaking or mechanical grates the grate could be deeper if it 
were otherwise desirable. 

277. The Bridge-wall. — The back of the ash-pit and of 
the furnace or fire-box is made by a low wall over whose top 
the gases and products of combustion are to pass. It sepa- 
rates this space in the setting from the combustion-chamber 
behind it. In so far as it is merely a separating wall it might 
be made of 8 inches in thickness, but inasmuch as with 




Fig. 458. 

stationary grates it is liable to suffer impact from the slice-bar 
in cleaning the top of the grates, it is more usual to give it a 
thickness from the bottom to the line of the grates of 2|- or 
even 3 bricks lengthwise, giving a dimension of from 20 to 24 
inches. It is not necessary that at the top it should be of 
this full width, and therefore it is quite usual to taper it from 
the line of the grates backwards, either from the front or from 



BOILER-SE TTING. 



539 



the back, so as to give it a width of one brick or 8 inches 
only at the top. Examples of both methods of tapering will 







be found in the illustrations Figs. 436 to 461. The objec- 
tion to tapering from the front or fire-box side is that so much. 



540 MECHANICAL ENGINEERING OF POWER PLANTS. 

of the fire as lies upon the sloping surface does not receive its 
full proportion of air, although this is corrected in part by the 
slanting direction which the air takes in passing from the 




grates to the top of the bridge. The diminished thickness at 
the top is of advantage in diminishing the friction of the gases 
in passing over the bridge, and in rendering it unlikely that 
misdirected fuel will be caught upon it. It will be observed 



BOILER-SETTING. 541 

also that there is difference of practice as to making the top 
of the bridge-wall a horizontal line, or an inverted arch 
parallel to the circumference of the shell. The inverted arch 
is supposed to direct the currents of hot gas and flame close 
to the shell. It makes, however, a very deep corner where the 
height from the grate-surface is so much greater than at the 
middle. The horizontal wall is easier to make, keeps the fire 
of equal intensity over its whole width, and the tendency of 
hot gas and flame is to keep to the upper part of its passage 
in any event. 

The bridge-wall is represented as solid in the foregoing 
illustrations: it is quite common to perforate its rear at or 




Fig. 461. 

near its top, and to make openings into a hollow within it to 
which air can have access from the outside. The draught of 
the chimney will draw air in through this hollow wall, where it 
will become heated by contact with the hot bricks, and pass- 
ing through the opening will mix with the flowing products 
of combustion over the top, and help to complete their com- 
bustion (Fig. 462). With this same purpose the bridge-wall 
is often made of a hollow cast-iron box with similar per- 
forations at its back. It will be seen also that a metallic 
bridge-wall may be filled with water to be evaporated, and, if 



542 MECHANICAL ENGINEERING OF POWER PLANTS, 




BOILER-SETTING. 543 

proper circulation is kept up within it, it can form an efficient 
addition to the heating-surface. If water-grates are to be 
used in a brick setting, the water bridge-wall becomes, practi- 
cally, a necessity. 

278. The Combustion-chamber — Behind the bridge-wall 
and underneath the shell of the boiler is an open space in- 
tended to permit complete combustion of the carbon which 
may come over the bridge-wall in the form of flame or com- 
bustible gas. For this reason it is called the combustion- 
chamber, even if, as is the case in anthracite practice, there 
is really no combustion to take place within it. It is desira- 
able to have it with gas-fuels in order that a space may be 
made in which the boiler shall not be too closely forced into 
contact with the hot gases and extinguish them by its lowered 
temperature, and, furthermore, in which there shall be per- 
mitted both room enough and time enough for a proper union 
of oxygen with the gases. It is furthermore of advantage, if 
otherwise practicable, to introduce refractor}/ bricks or sim- 
ilar material into this combustion-chamber which shall serve 
to keep up the temperature of the flame and gases above the 
point below which no chemical union can occur. In anthracite 
practice this chamber can be filled up in part or largely with- 
out disadvantage. In bituminous practice this would cause a 
smoky and wasteful combustion. Fig. 463 shows a type of 
a setting prevalent at one time in which the small size of the 
combustion-chamber may be credited with causing very smoky 
chimneys. The combustion-chamber serves also as a catch- 
chamber to hold some of the particles of ash and flue-dust 
which will be drawn out of the fire by a strong draught, but 
which will be precipitated by the lower velocity of the gas- 
currents in the large area behind the bridge-wall. This makes 
it necessary that there should be doors of access into the com- 
bustion-chamber, that it may be cleaned out at intervals, and 
such doors give also a convenient access for inspection of that 
part of the boiler. These doors will usually be of some size 
(perhaps 18 or 24 inches wide by 18, 24, or 36 inches high), 
and they will be made by building a flanged framework of cast 



544 MECHANICAL ENGINEERING OF POWER PLANTS, 




G 



a 



Q. 



Q 



m 






BOILER-SETTING. 545 

iron into the brick-work which will clasp the flange, and be sup- 
ported by them while the projecting plane beyond the brick- 
work carries the hinges (see H in Fig. 443). The door-open- 
ings are objectionable, because they break the continuity of 
the brick wall and cracks originate from them for this reason. 
It would be desirable not to put them at the bottom on 
account of this tendency to create cracks, which are less 
troublesome if they are towards the top. The location of the 
doors in the side or back wall of the combustion-chamber 
must be a matter of convenience and location, but the back 
wall is not as good a place as the sides by reason of the effect 
of direct impact of flame and gases. 

In sectional-boiler settings the combustion-chamber is 
partly filled by the boiler itself, or rather it is made from a 
space within the tubes. The absence of return fire-tubes in 
boilers of this class compels the gases to receive a circuitous 
path in and out among the water-tubes, and this is secured 
by partitions of fire-brick like hanging bridge-walls, which 
compel the gases to pass around them and meet complete 
combustion while still in contact with the tubes. It is 
probable that the gases will be hotter when leaving a sec- 
tional boiler than in leaving a return tubular boiler for these 
reasons. 

279. The Back Connection. — The hot gases passing back- 
wards underneath the shell of the boiler are to be deflected 
into the tubes or flues in order to come forward through them 
to the front. Following the analogy of the internally-fired 
boilers, this space at the back end of the setting in which the 
tube sheet comes has been called the back connection. It is 
apt to be about 2 feet deep, and must be roofed at the top at 
such a level that the flame and hot gases impinging against 
the back head shall not heat the surface of that head, which is 
not protected from overheating by water on the inside. It 
will be seen from examination of Figs. 436 to 462 that there 
are three methods for making this roof of the brick connec- 
tion. 

First, the roof may be made of an arch whose axis is 



54^ MECHAiVICAL ENGINEERING OF POWER PLANTS, 

transverse to the setting, and of which the boiler itself shall 
form the keystone and take the thrust of the arch (Fig. 436). 

Second, the roof may be flat, the bricks which form it 
being supported upon transverse bars of cast or wrought iron 
which rest upon the side walls and support the bricks. Cast 
iron is better than wrought from its resistance to softening 
by heat, and the usual shape is a T iron with its cross down- 
wards, and the web of the T among and between the bricks 
(Fig. 442). 

The third plan is to sprirtg a very flat arch across between 
the side walls. The objection to this is that so flat an arch, 
if its rise at the centre is so little as not to uncover the water- 
line of the boiler, is a construction which is difificult to make, 
and which heat is sure to deteriorate. 

If the first method is used, the back end of the boiler must 
be' the fixed end, and expansion be from this end towards the 
front. The back connection must be large enough to give 
convenient access to the back head of the boiler for any 
repairs which may be called for at that point. 

280. The Front Connection. — The gases which pass 
through the flues or tubes are to be gathered together at the 
front head and discharged into the stack. When the front 
end is not made a smoke-box it will be called the front con- 
nection. The gases should have parted with a great deal of 
their heat in passing through the flues or tubes, so that their 
volume is less, and for this reason the front connection is 
usually about two thirds the depth of the back connection. 
Sectional boilers have no front connection, but the gases pass 
directly from the back connection to the stack. The front 
connection gives access to the front head of the boiler, and 
the flue-doors of the boiler-front admit to it from the outside. 

281. The Flue to the Chimney-stack. — When the front 
connection is a smoke-box in extended front settings, and in 
many cases of full front settings, the gases pass directly 
through an opening into a metallic flue which carries the 
products of combustion to the chimney and so to waste. If 
there are several boilers side by side or in a battery, short 



BOILER-SE TTING. 



547 



lengths of flue from each front connection or smoke-box will 
unite them to a larger flue increasing in size as additional 
quantities of gas are discharged into it, and through this 
common flue they pass into the chimney (Fig. 464). 




When the chimney is at the back of the setting a cus- 
tomary arrangement has been to carry the gases to the rear 
in a flue formed by springing an arch over the top of the 
boiler from side wall to side wall. The tie-rods and buck- 
stays withstand the thrust of this arch, and from the space 



54S MECHANICAL ENGINEERING OF POWER PLANTS. 

thus formed the gases pass to the chimney. Fig. 436 shows 
this arrangement clearly. 

It offers the following advantages: 

(i) Radiation is diminished from the top and the boiler is 
kept warm by its own gases. 

(2) If these gases are hot enough, they have a tendency to 
dry or even slightly to superheat the steam in the steam-space 
and in the dome. 

The objections to this construction are: 

(4) It is of small value as a superheating appliance, because 
shortly after starting the boiler is thoroughly covered with a 
coating of fine ashes or dust which is practically a non-con- 
ductor. 

(5) It is difficult to construct the opening through which 
the dome of the boiler must protrude, and the expansion of 
the boiler in the brickwork opens cracks for leakage of air 
into the flue. . 

When, however, the chimney must of necessity be at the 
rear of the setting of such boilers, these difficulties can be 
avoided sufficiently well to make it a justifiable feature of the 
setting. It should be large enough to permit the access of a 
man for inspection. 

Where it is not used, the top of the boiler will be covered 
with some non-conducting material laid on in sections v/hich 
shall permit their removal for inspection. These non-con-- 
ducting coverings catch and hold any water of leakage, and 
unless care is taken may occasion external corrosion. 

282. The Pamper and Damper-regulator. — In order to 
control the action of the chimney, which depends on the 
weight of a column of air outside of it, a valve of some sort 
is required in the flue from the boiler. When closed wholly 
or in part it causes a friction in the discharge of the gases 
through it, which checks the flow of air through the fire. 

It is usually made in one of two forms. The sliding or 
guillotine damper is a flat plate sliding in grooves across a 
frame in the flue (Fig. 436). The pivoted or balanced dam- 
per is a plate mounted upon an axis through its centre of 



BOILER- SE 7^ TING. 



549 



gravity by which it can be turned so as to stand edgewise to 
the flow of gas, opposing Httle resistance, or flatwise to it so 
as to close the opening altogether. The sliding damper 




Fig. 465 
•usually is the harder to move, and if it slides vertically has to 
be counterweighted in order to be balanced. The other form 
is in equilibrium in any position. The damper is often 
arranged not to close entirely even when it is nominally shut, 
in order that there may still be a tendency for a current to be 
maintained inwards through the setting, and out through the 
stack to prevent undesired gases from getting into the boiler- 
room because access to the chimney is closed. 

Since the chimney is the immediate and usual method of 
controlling the fire, it becomes exceedingly simple to m_ake it 
automatic, so that the fire shall be somewhat self-regulating. 
The pressure of steam can be brought against a piston, and 
the motion caused by that pressure can be resisted by a 
weight or spring. When the pressure exceeds the normal, the 



5 so MECHANICAL ENGINEERING OF POWER PLANTS. 

weight will be overcome; when it falls below the normal, the 
fall of the weight will move the piston the other way. The 
motion of the piston, which can also be made a diaphragm of 
flexible metal, can be attached to the damper so as to close 
or open it when the pressure rises or falls. This may be done 
either directly, as in some of the older forms of damper-regu- 
lation (Fig. 465), or the steam-pressure may move a valve to 




Fig. 466. 

admit the pressure which operates the damper, upon one side 
or another, of the mechanism which moves the latter (Fig. 
466). This may be the water-pressure of the city mains, or 



BOILER- SE T TING, 551 

it may be the pressure from the boiler of the steam or water 
in the boiler itself. 

283. The Chimney. — The chimney is a thermodynamic 
machine for producing the movement of gas within it on the 
principle of an inverted siphon, whose long leg is the heavy 
column of cold air outside of the chimney-stack, and whose 
short leg is the column of warm light air within it. While 
these columns are of the same length, they are of unequal 
weight by reason of the difference of the weight of each cubic 
foot which results from the difference in temperature. It will 
be aside from the present purpose to discuss the chimney 
theory, but practice seems to agree that a cross-section of one 
eighth of the grate-area is about the proper size, which leaves 
the height of the chimney the quantity to be determined. 
Practical conditions in cities often fix this limit independent 
of theory and rational design, and a formula which has been 
found to correspond very closely with conditions which have 
proved satisfactory is as follows: 

In this E denotes the effective area, and is equal to the net 
area, ^ — ^ of the square root of itself, or^ = ^ — 0.6 ^ A. 
This is apparent by assuming that the friction of the gases in 
the chimney withdraws from the total area a narrow edge 
having a depth of 2 inches in a radial direction. 

The discussion of chimney-foundations and their stability 
against wind belongs to another branch of the subject. 

The construction of chimneys may be of three types. 
First, brick, round or square; second, of wrought iron or 
steel plate with a brick lining in whole or in part; and third, 
a simple plate-iron stack unlined. The round brick stack is 
lighter than the square stack, and is less affec-ted by wind- 
pressure. It is also in most designs more pleasing to the eye. 
The form of stack with a ground-plan resembling a star has 
been much used in certain parts of the country, and offers the 
stability given by such buttressed construction. The iron or 



552 MECHANICAL ENGINEERING OF POWER PLANTS. 

r«r--s'o--> 




Fig. 467. 



BOILER-SETTING. 553 

steel stack is more efficient in cold climates by reason of per- 
mitting less infiltration of air, and it can be constructed by use 
of proper anchor-bolts so as to need nothing to stay it against 
the wind. The iron shell without the weight of the lining 
will be required to be guided or stayed, and special care is to 
be taken that one of the four or six wire-rope guys should be 
in the direction of the strongest prevailing wind. Such guys 
should be attached two thirds of the distance up the chimney. 

Access should be permitted to the chimney at its base 
through a proper door either in the flue or in the foundation 
of the chimney, and it is best that a ladder on the outside of 
the chimney should give access to its top. In a square chim- 
ney this ladder can be made by bars let into two walls at a 
corner inside. The top of the chimney is exposed to action 
by frost and snow, which throws down the brickwork at the 
top, and forms a reason why the best results are attained by 
building the chimney with a metallic or stone covering, so as 
to prevent moisture from getting into the joints. Figs. 467 
and 468 show chimney constructions and the proportions 
which have been found satisfactory, according to which the 
thickness may be reduced as the chimney attains height. 

284. Artificial Draft. — Since the chimney is a machine or 
appliance for putting air in motion through the grate, setting 
and flues and the chimney itself, that same result can be 
attained by mechanical means. A calculation of efficiencies 
shows that for heights of chimneys such as are ordinarily used 
the mechanical methods of securing draft are the more effici- 
ent, so that it becomes a question of consideration whether 
the necessary air for combustion shall be furnished by a costly 
chimney or group of them, or by a continuously running 
m.achine of some selected type. 

Artificial draft can be secured by two general methods. 
The first type is that made familiar in locomotive practice, 
in which a rapid motion is given to the air to draw it out 
of the smoke-box so that the reduction of pressure within 
the latter shall cause a flow through the grates, fire, and 
tubes to equalize this rarefaction. The other plan is to 



554 MECHANICAL ENGINEERING OF POWER PLANTS. 

cause a pressure of air in the ash-pit below the grate-bars sa 
that the air will flow up through the fire, the setting, and flues 
by the excess of pressure which prevails in the ash-pit. This 
is called the forced-draft system, and is usual in high-speed 
marine practice. The movement of the air can be produced 
either by means of a steam-jet inducing a current of air to 
flow, or fans or blowers either of the centrifugal or positive 
type may be used. If the first or aspirating principle is used, 
the products of combustion must pass over the aspirating 
appliance. These gases are hot and possibly corrosive. The 
heat makes lubrication difficult, and almost excludes the use 
of apparatus where lubrication must be provided unless all 
bearing-surfaces can be without the flues which carry the gas. 
Protection against corrosion can be secured if proper trouble 
is taken, but where this is not guarded against the apparatus 
deteriorates rapidly. The forcing system has the fresh cool 
air pass through the forcing appliance, and has furthermore 
the advantage of maintaining a higher tension within the 
setting than prevails outside of it, so that there is little or no 
tendency for cool air to leak through cracks or porous brick- 
work into the gas-currents. This is a difficulty present 
where the draft is done by aspiration. On the other hand, 
the pressure system makes a hot and gassy fire-room if there 
are places where gas can escape through cracks or elsewhere 
from within the setting into the room. Since combustion is 
more efficient the denser the air used to effect it, the pres- 
sure system offers an advantage from this point of view, as 
compared with natural draft or the aspiration system. 

285. Advantages of Artificial Draft. — It is to be said 
in favor of natural or chimney draft that, when the chimney 
is once built and paid for, the draft-machine costs nothing 
to run except the heat which is used for this purpose, and it 
undergoes little or no deterioration with use. Furthermore, 
in cities the necessities imposed upon the power plant to 
carry the products of combustion high enough up to create no 
nuisance in its neighborhood compel a height and cost of 
chimney which make the consideration of artificial draft 



BOILER-SETTING. 55S 

unnecessary, since the high chimney must be there in any case. 
Again, where the plant is so large that the cost of the draft- 
machine becomes considerable, or, what is the same thing, the 
cost of the expensive chimney becomes distributed over a 
large number of horse-power units, the advantages of artificial 
draft are not so apparent. 

Artificial draft, on the other hand, offers the following 
advantages: 

(i) The rapidity of combustion in the fire-box is not 
limited by atmospheric conditions. 

(2) It is possible to increase the evaporative capacity of a 
given plant without other change than the velocity of the 
draft-machine. This increase may be either permanent or 
to meet sudden demands for steam, such as occur in street- 
railway practice at busy hours. With natural draft the 
chimney must be designed to meet the maximum requirement^ 
and will be partly shut off at other times. 

(3) It is possible to burn inferior, cheaper, and smaller 
sizes of fuel with artificial draft, because a high pressure 
can be maintained which will force the necessary air through 
a compact body of fuel. 

(4) Where high stacks are not made necessary the cost 
which they entail is avoided, or is offset by a less cost of 
the draft-machine. 

286. Disadvantages of Artificial Draft. — The objections 
to be raised against the artificial draft are: 

(i) The running cost of the machine. While it takes less 
coal than the chimney to do a given work, the fuel is not the 
only expense where an engine must be run consuming oil and 
other supplies, and calling for repairs and supervision. 

(2) The artificial-draft machine occupies space which can 
often be ill spared. 

(3) Running machinery, and particularly that at high speed 
such as most draft appliances demand, is rarely silent, is often 
noisy, and is liable to breakdowns which compel it to stop. 

It will be seen that chimney-draft is not liable to these 
disadvantages. 



55^ MECHANICAL ENGINEERING OF POWER PLANTS. 

The machine for causing the draft may be a centrifugal 
fan driven either by its own directly-coupled engine, or by a 
detached engine, or a revolving shaft, or by means of an elec- 
trical motor. The positive blowers will be driven by belts or 
engine, whether used for pressure or suction methods, and the 
steam-jet, which is the third appliance, requires no moving ma- 
chinery when used in either system. It will be seen that each 
of these offers some advantages and disadvantages of its own. 
The fan method, if driven by belting, increases the running 
cost; and if electric current must be generated, the cost of its 
transformation must be considered. The steam-jet plan 
occupies very little space, and is cheap to buy in the fixst 
instance. It is, however, wasteful of steam as compared with 
the other systems, and is in most cases too noisy. If used 
as a forcing system, the steam passes through the fire and is 
objectionable. If used as a suction system, the steam goes 
out with the products of combustion and does no harm. 

The artifical-draft system is a feature of the automatic 
stoker shown in Fig. 453 and in some others, and it offers the 
advantage that the steam-pressure can be made to act upon 
the draft machinery directly and produce a more prompt 
and efficient effect upon it than when that pressure acts upon 
the chimney only and through a damper-regulator (par. 282). 
The fall of pressure in natural draft can only open the chim- 
ney wide and attain at best the full effect of the entire chim- 
ney. By acting on the machinery of artificial draft the fall of 
pressure can be made to stimulate combustion above the 
normal rate, and with great promptness. 



CHAPTER XXV. 

THE BOILER-FURNACE AS THE ORIGIN OF POWER. 

287. Calorific Power of the Fuel. — It has been said (par. 
270) that the boiler-furnace and its design condition every 
other detail of the power plant, because here the energy stored 
in the fuel is liberated in the form of heat generated by com- 
bustion. This heat is transferred to the metal of the boiler 
and to the water within it, and appears in the form of a ten- 
sion or pressure of the steam-gas which is used to drive the 
piston in the engine. It is obvious, therefore, that the 
number of units of heat resident in a unit of weight of the 
fuel burned in the furnace measures the capacity of that fur- 
nace for furnishing power to the engine. In British units the 
calorific power of a fuel is the number of pounds of water 
which will be raised one degree Fahrenheit by the burning of 
one pound of the fuel. The values of different fuels for 
power purposes will therefore depend upon their calorific 
power. This calorific power may be determined theoretically 
by means of an analysis which shall give the weight of carbon 
and hydrogen present in each pound, but a more satisfactory 
determination is that made by an instrument, called a calorim- 
eter, in which coal is burned in such a way that all the heat 
given off in combustion is caught and measured. It will be 
obvious that a given weight of a fuel containing a considerable 
percentage of incombustible matter or ash will not be able to 
evaporate as much water as one which has nearer 100 per cent 
of combustible. The following table presents accepted gen- 
eral values for the calorific power of various fuels. 

557 



558 MECHANICAL ENGINEERING OF POWER PLANTS. 



w w 

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O W H 

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THE BOILER-FURNACE AS THE ORIGIN OF POWER. 559 

288. Force Corresponding to the Combustion of One 
Pound of Fuel. — If the same British units be used, it will be 
apparent that the foot-pounds of energy resident in any fuel 
will be the product of the calorific power above given multi- 
plied by the number of foot-pounds which correspond to a 
unit of heat. 

It will be recalled from Chapter I that the accepted value 
for this number is 778. If the product then of the calorific 
power by 778, giving a total in foot-pounds, be divided by the 
number of foot-pounds corresponding to a horse-power, or 
33,000, the quotient will be the horse-power theoretically 
resident in a pound of fuel. It is, however, impossible to 
realize all the heat in the coal, for several practical reasons. 

(i) Some of the heat has to be wasted so far as steam- 
making is concerned, in order to create an upward draft in 
the chimney at a velocity sufificient to maintain combustion in 
the fire. 

(2) A portion of heat is consumed in raising the tempera- 
ture of the air which passes through the fire, for combustion 
and for dilution, and the greatest waste is that caused in 
bringing the inert nitrogen of the atmosphere to the temper- 
ature of the hot gases. 

(3) The ash or incombustible mineral matter in the coal is 
heated, and what goes off in this way is wasted. 

(4) In externally-fired boilers, set in brick, there is a loss 
and waste by the radiation from the setting and by conduc- 
tion. 

(5) Where combustion is incomplete so that the combus- 
tible gas or smoke is allowed to escape past the heating-sur- 
face of the boiler from bad design or bad management, just so 
much valuable heat is wasted. 

(6) Transfer of heat is not perfect. 

It is apparent that these losses are furnace-losses and have 
nothing to do with the further series of losses caused by the 
use of steam as a vehicle to carry the heat into the engine- 
cylinder. Instead, therefore, of being able to get a horse- 
power with about two-tenths of a pound of coal as the theo- 



560 MECHANICAL ENGINEERING OF POWER PLANTS. 

retical calculation above made would indicate, the best 
results of practice give the horse-power with 1.25 pounds of 
coal, and from this superior figure the less satisfactory per- 
formance of uneconomical plants brings the figure up to 3 or 
even 5 pounds of coal to the horse-power per hour. 

289. Heat of Combustion in the Furnace. — The defini- 
tion of calorific power given above gives a value which is inde- 
pendent of the time required or given for the combustion to 
take place. In actual practice, however, the temperature 
prevalent in the furnace is entirely dependent upon the 
rapidity with which the combustion takes place. With a high 
rate of combustion the fire is hotter than when the fuel burns 
slowly, and theory and practice both indicate that the best 
results will be obtained, other things being equal, when the 
temperature is very high in the fire, provided that sufficient 
heating-surface be present in the boiler to cool the gases in 
contact with it before they leave the setting. These condi- 
tions of intense combustion and high temperature are those 
which belong to the conditions of forced draft, and point to 
the necessity for very extended heating-surface where forced 
draft is to be used. If the gases go off hotter than they ought 
to be when they leave the setting, heat is being wasted which 
ought to have been caught and used to make steam or heat the 
water. The element of time, furthermore, is of importance 
in a practical way, because any given weight of gas carries a 
certain number of heat-units through the gas-flues in the 
setting, and if this gas does not meet condensing-surface 
enough to be cooled, its full capacity to evaporate water is 
not used. 

290. Pounds of Coal Burned per Square Foot of Grate- 
— It is customary to state the intensity of combustion which 
measures the temperature of combustion, using as a unit the 
pounds of coal burned per square foot of grate-surface per 
hour. This measures the quantity of coal which will be 
charged into the furnace by the fireman, and, when taken in 
connection with the calorific power of the fuel, measures the 
horse-power or work-units which each furnace will furnish. 



THE BOILER-FURNACE AS THE ORIGIN OF POWER. 561 

It is apparent that the intensity of the draft measuring the 
quantity of air supplied for combustion exerts a vital influence 
on the coal which will be burned each hour, and furthermore 
that this is a question of practice and experience. 

The following table gives the accepted rates of combustion 
per square foot of grate as derived from observation of 
English practice, and are reliable data to start from. 



Rates of Combustion. 



With chimney draught : 



Pounds per Square Foot 
per Hour. 



Slowest rate, Cornish boilers 4 to 6 

Ordinary rate, Cornish boilers lO to 15 

Ordinary rate, factory boilers 12 to 18 

Ordinary rate, marine boilers 15 to 25 

Quickest rate for anthracite coal 15 to 20 

Quickest rate for bituminous coal 20 to 25 

With forced draught: 

Locomotives 40 to loa 

Torpedo boats 60 to 125 

The following table, prepared from careful collation of 
French experience by Morin and Tresca and first published 
by the late W. P. Trowbridge, indicates the rapidity of com- 
bustion which is to be expected with chimneys of the height 



Heights of Chimneys in Feet. 


Pounds of Coal per Square 

Foot of Section of Chimney 

per Hour. 


Pounds of Coal per Square 
Foot of Grate per Hour. 


20 


60 


7-5 


25 


68 


8.5 


30 


76 


9-5 


35 


84 


10.5 


40 


93 


11.6 


50 


105 


13 I 


60 


116 


14.5 


70 


126 


15.8 


80 


135 


16.9 


90 


144 


18.0 


100 


IS2 


19.0 


no 


160 


20.0 



562 MECHANICAL ENGINEERING OF POWER PLANTS 

given. This table also is of interest in connection with the 
design of chimneys, if it is desired to start with the combus- 
tion of a given weight of coal (par. 283). 

It must be recognized that these data are approximate, 
since the kind of coal, its percentage of ash, and the skill 
of the fireman are quantities which will produce great variation 
in figures of this sort. 

291. Pounds of Water per Pound of Coal Burned. — 
Since the steam-engine to be served by a boiler is to be 
supplied with a given weight of steam per hour to fill the 
volume of the cylinder a certain number of times per minute 
and per hour, the practical question as to the effectiveness of 
the furnace takes the form of the number of pounds of water 
which it will evaporate per hour. This is affected both by 
the temperature at which the water is admitted to the boiler 
and by the pressure with which it is withdrawn from the 
engine as steam. The duty of the coal is, first, to heat the 
water from the temperature of its admission as feed-water 
to the temperature at which water stands at the working 
pressure when making steam. Secondly, it must furnish the 
amount of heat-units required to transform water at that 
temperature and pressure into steam at the same pressure; 
and thirdly, it must do the external work of expanding the 
water into the much greater volume which it will occupy as 
steam. 

It is the function of steam-tables to give the total quantity 
of heat which belongs to steam at different pressures; but it 
will be apparent that if the calorific power in heat-units of any 
fuel be divided by the heat-units resident in a pound of steam 
at the pressure in question, the quotient will be the number 
of pounds of water which can be evaporated theoretically by 
one pound of coal having the given calorific power. A calcu- 
lation made on this basis with the foregoing calorific powers 
indicates that rarely will a fuel be found which will evaporate 
over 15 pounds of water per pound of coal, and, furthermore, 
practice with the limitations imposed makes it very unusual 
to reach 12 pounds of water per pound of coal. Ten pounds 



. 



THE BOILER-FURNACE AS THE ORIGIN OF POWER. 563 

is excellent practice, and 7 pounds would be a more usual ex- 
perience in most places. 

292. Pounds of Water per Horse-power per Hour. — 
Since the capacity of the steam-engine for doing work is 
measured by the amount of heat which it will receive from 
the fire through the water and steam, it is apparent that the 
higher the pressure of the steam which enters the cylinder, the 
more power it will receive for a given weight of steam fur- 
nished to it. This explains the increasing use of high-pressure 
steam, and will explain also the diminishing weight of water 
which is required to furnish a horse-power in the engine-cylin- 
der. The old figure of James Watt's period was a cubic foot 
of water, or (y2\ pounds of water, per horse-power per hour. 
The standard which was introduced first at the tests made in 
1876, at the Centennial Exhibition, was that an engine of that 
period should give a horse-power with 30 pounds of water, 
and from that standard what has been called the horse-power 
of the boiler was derived, w^iich has a certain present accept- 
ance. The boiler horse-power is to be defined as the ability 
to evaporate 30 pounds of water received in the boiler at a 
temperature of 100° Fahr. into steam at 70 pou*^ds pressure 
above the atmosphere under ordinary conditions of use and 
practice. The quantity of heat demanded to evaporate a 
pound of water under these conditions is 11 10.2 British 
thermal units. This is the same as i\\ pounds of water 
evaporated into steam at that temperature from a feed-tem- 
perature of 212° Fahr. Improvements in the steam-engine, 
added to the use of higher pressures and better construction, 
make this allowance of 30 pounds per hour per horse-power 
unnecessarily large for economical engines and of large size. 
Recent improvements show that the horse-power can be 
obtained with considerably less than half that weight of 
water, and designers are aiming to get an engine which 
shall give a horse-power with 13 pounds for prevailing 
pressures, and less with the use of unusually high pres- 
sures. The following table gives certain figures from test 
and experiment: 



5^4 MECHANICAL ENGINEERING OF POWER PLANTS, 



b 


e 


/ 


e 


f 




Type of Engine. 


Feed Water per Indicated Horse-power per Hour. 




Non-condensing. 


Condensing. 


Per 

Cent 
Gained 


Name. 


Probable 
Limits. 


Assumed 

for 
Compari- 
son. 


Probable 
Limits. 


Assumed 

for 
Compari- 
son. 


by Con- 
densing 


Simple high-speed 

Simple low-speed 

Compound high-speed. . . . 

Compound low-speed 

Triple high-speed 

Triple low-speed 


lbs. 
35 to 26 
32 to 24 
30 to 22 

27 to 21 


lbs. 
33 
29 
26 

¥: 
24 


lbs. 
25 to 19 
24 to 18 
24 to 16 
20 to I2f 
23 to 14 
18 to I2f 


lbs. 
22 
20 
20 

18 

17 
16 


33 
31 
23 
25 
29 



* The table does not give a water rate for the compound low-speed non- 
condensing engine, but it may be fairly assumed to be about the same as for 
the triple high-speed non-condensing engine, namely, 24 pounds. This will 
make the gain by condensation just twenty-five per cent. 

The terms " high speed " and " low speed " refer to the number of revo" 
lutions per minute, and not to the piston-travel. Low-speed engines are 
Corliss engines and the like, with releasing cut-offs, and have a rotative 
speed usually less than 120 revolutions per minute. 

293. Transfer of Heat. — The heat generated in the boiler-^ 
furnace is to be absorbed first by the metal of the heating- 
surface, and conducted by the latter to the water which it 
contains. The heat of the fire can be transferred to the metal 
of the boiler by radiation and by contact. Radiation is the 
most effective method of transferring heat, and is the method 
when solid and incandescent matter is so placed relatively to 
the heating-surface that waves of heat-motion from the hot 
body strike the cooler body and are absorbed by it. Contact is 
the method of transfer from a hot, but not glowing, gas which 
touches the surface of the cooler body and imparts its heat 
by such contact. The solid matter glowing in the current of 
the gas makes a flame, and such flame heats by radiation. 
When the combustion is complete the gas becomes non- 
luminous, and its heat must be absorbed by contact. Short- 
flame fuels heat by radiation from the solid matter in the 
fire-box, but by contact entirely behind this point. It is the 
flaming capacity of soft coal which gives it its value as a 



THE BOILER-FURNACE AS THE ORIGIN OF POWER. 565 

steam-making coal ; but if used with tubes so small as to extin- 
guish the flame before combustion of the carbon particles is 
complete, some of its effect is lost. 

When the heat is absorbed by the heating-surface, and 
conducted to the water, the latter receives and transfers the 
heat throughout its body by convection. Currents of descend- 
ing cold water and ascending warm water carry the heat 
received at the heating-surface up through those parts of the 
water which are not in contact with the shell. The impor- 
tance of circulation, which measures the rapidity of this process, 
is thus apparent. The effect of the thickaess of the plate of 
the heating-surface becomes apparent when it is considered 
that all transfer of heat is rapid and efficient in proportion as 
the difference of temperature is great between the heated and 
the cold body. If the conducting metal is thick, the water 
does not cool the outer surface so efficiently, and therefore 
it does not withdraw the heat from the gases or the flame as 
efficiently during the period in which the flame or gas is acting 
upon the water. 

294. Ratio of Grate-surface to Heating-surface. — It will 
be apparent that the heating-surface, which is the absorbing 
surface of the boiler, should be proportioned with respect to 
the initial temperature of the fire, which is dependent upon 
the draft, and also with respect to the fuel to be used, and 
with respect to the dependence mainly upon radiation or con- 
tact for transfer. 

It will further be apparent that this ratio should vary with 
the type of boiler and the arrangement and relative efficiency 
of the heating-surface for absorbing heat. The making of 
boilers as a business, and often in ignorance of the exact con- 
ditions in which they are to be used, has resulted in a certain 
accepted ratio between the grate-surface, which measures the 
total amount of heat supplied to a boiler, and the heat- 
ing-surface by which that heat is to be absorbed. The 
following table presents accepted relations between these 
quantities: 



566 MECHANICAL ENGINEERING OF POWER PLANTS. 

RATIO OF GRATE-SURFACE TO HEATING-SURFACE: 

Marine return-tube boilers i : 25 to i : 38 

Marine return-tube boilers, average of a large number 

of boilers. i : 30 

Lancashire boilers i : 26 to i : 33 

Cornish boilers i : 27 to i : 34 

Boilers of modified locomotive type i : 30 to i : 34 

Yacht boilers, locomotive type i : 40 to i : 46 

Horizontal internally-fired cylindrical multitubular 

boilers i : 45 to i : 50 

Portable boilers, locomotive type i : 23 to i : 70 

Water-tube boilers o . . i : 34 to i : 65 

Locomotive boilers i : 60 to i : 70 

It is usual to consider that the entire area of the fire-tubes 
and flues is available for heating, although there is no ques- 
tion that their upper surfaces are the more efficient. The 
lower surfaces of horizontal water-tubes are more efficient 
from a like reasoning, and the front sides of vertical water- 
tubes. 

In boilers of the internally-fired type, and particularly in. 
those of the locomotive class, the withdrawal of heat from 
the gases by the tubes is very much more rapid at the first 
end at which they enter than towards the end at which they 
leave. Experiments have been made by dividing the boiler 
into sections with proper diaphragms and measuring the evap- 
oration in these several sections. The following table indi- 
cates how much more efficient the sections nearest the fire-box 
prove themselves to be: 

Section number , I 2 3456 

Percentage of C Test No. i 47 23 14 8 5 3 

evaporation ( '' '' 2,... 65 29 16 13 10 

295. Evaporation per Square Foot of Heating-surface. 

— The experience of boiler-designers shows that for maximum 
economy a boiler should be proportioned to have one square 
foot of heating-surface to every three pounds of water to be 
evaporated into steam at atmospheric temperature from a 
feed-water temperature of 212° Fahr. This is the basis for 
the usual figure of i ij- to 12 square feet of heating-surface 
per horse-power. This must be taken, of course, as an aver- 



THE BOILER-FURNACE AS THE ORIGIN OF POWER. $6 J 

?,ge figure and as corresponding to ordinary conditions, and 
susceptible of being modified with higher furnace-temperature 
and any other variables. 

296. Pounds of Air Required per Pound of Coal. — It is 
usual to consider that a furnace-temperature caused by com- 
bustion is to be theoretically calculated by finding the relation 
between the calorific power of coal and the absorptive 
capacity for heat of the products of combustion. When, 
therefore, unnecessary amounts of air are introduced through 
the fire or above it, their tendency is to lower the furnace- 
temperature, and it' becomes desirable to know what is the 
least weight of air which will secure complete combustion. 
This is found by finding the weight of oxygen required to 
combine chemically with the carbon of the fuel, according to 
their atomic weights, and then to find the weight of air which 
contains this weight of oxygen. The calculation shows that 
a pound of carbon requires 2.66 pounds of oxygen, and this 
makes the volume of air necessary to burn one pound of 
carbon to be 140 cubic feet at 32° Fahr., which is equivalent 
to 1 1.3 pounds of air, which is usually called 12. Much 
more than this is demanded, however, because the carbonic 
acid, which is the resulting product of combustion, is not a 
supporter of such combustion, but must be diluted with at 
least half as much again or twice as much free air in order 
that combustion may be maintained. With a fuel contain- 
ing hydrogen a larger volume of air is required from the 
greater weight of oxygen called for, and this explains the 
greater volume of air which hydrogen demands for its com- 
plete combustion. It is an advantage of forced draft that it 
makes less important this diluting excess of air, and conse- 
quently favors maintaining a high temperature in the furnace. 

297. Oil as Fuel. — The exceeding convenience of petro- 
leum in some of its forms as a fuel which can be mechanically 
handled with ease, and which has a high calorific power, has 
induced experiments in its use. The usual method is to 
supply it in a state of vapor in which the finely divided par- 
ticles of the oil are drawn into the furnace-area by the prin- 



568 MECHANICAL ENGINEERING OF POWER PLANTS. 

ciple of induced currents. High-pressure air or steam passing 
through annular openings draws the oil up and finely divides 
it into a spray, and the mixture of oil and air or oil and steam 
is ignited within the fire-box. Intense combustion follows, 
so much so that it is often found that it will not answer to let 
the flame impinge directly upon the heating-surfaces, as it 
erodes them away. The impact of the flame-current is usually 
received upon fire-brick or similar refractory material, which 
becomes white-hot and serves to insure ignition of the oil- 
vapor and a high temperature of the air used for combustion. 
The oil used is either the crude petroleum as it comes from 
the oil-well, or it is the product known as fuel-oil, which is 
the residue after the lighter elements of petroleum have been 
removed by distillation. The naphtha, gasoline, and kerosene 
are removed by a fractional distillation, and the less volatile 
residue is used to burn. 

298. Advantages of Boiler-firing with Oil. — The use of 
oil as a fuel under steam-boilers offers the following advan- 
tages: 

(i) Oil Jias usually a higher calorific power than solid coal, 
and consequently more evaporation can be gotten from a given 
boiler. 

(2) Oil being a liquid is handled mechanically and offers 
all the advantages of mechanical stoking with the simplest 
machinery and with no grates. 

(3) Oil has no ashes with the labor incident to their 
removal, and the possible expense in many places. It some- 
times leaves a residue, however. 

(4) The fire can be controlled instantly from its maximum 
intensity down to nothing by cutting off the supply, and a 
full fire can be started at once as soon as the oil is turned on. 
This adapts oil-firing for locomotive practice, and for any place 
where wide variations occur in the demand for steam. With 
solid-fuel firing, when the coal has once been charged into the 
furnace it must burn itself out. 

(5) The combustion can be made practically perfect, and 
therefore smokeless. 



THE BOILER-FURNACE AS THE ORIGIN OF POWER, 569 

(6) The liquid fuel gives off no sparks of solid burning 
material to be pushed through the stack to fall on combustible 
material and set fire to it. 

(7) The mechanical stoking feature reduces the labor cost 
for firing, and makes the fire-room work that of supervision and 
attendance. 

(8) It makes no dust. 

(9) Its smokeless combustion has a significance for war- 
vessels, since it enables them to move without betraying their 
presence, if out of sight below the horizon. 

(10) The operation of taking on fuel, and the storage of 
fuel at storage stations, is simplified and cheapened. 

(11) From the less frequent opening of the fire-door, and 
the maintenance of a constant temperature in the fire-box, it 
lasts longer and the cost of repairs is diminished. This is also 
of advantage to the boiler itself. 

(12) There is no loss of fuel in banking fires between the 
times that steam is needed, nor losses from fuel in the ash-pit. 

299. Disadvantages of Firing with Oil. — There are cer- 
tain objections to the use of oil v/hich have prevented its 
general adoption. 

(i) The use of crude oil with the volatile elements still 
remaining in it is prevented by city ordinances or fire depart- 
ments in many places. In others the fire restrictions compel 
special methods for holding the supply of oil which are some- 
times inconvenient to comply with. The oil must be below 
ground and so placed that it cannot flow out of its reservoir in 
case of conflagration and carry destruction to other buildings. 

(2) The crude oil has an offensive odor, and its use is pre- 
vented by the health boards of certain cities for this reason. 

(3) The vapor which escapes from crude oil forms an 
inflammable or explosive mixture with air. 

These considerations prevent or restrict the use of crude 
oil, and compel the use of fuel-oil as the form in which oil 
firing shall be possible. As the result of this — 

(4) It happens usually that oil-firing is costly as compared 
with coal. 



570 MECHANICAL ENGINEERING OF POWER PLANTS. 

(5) The supply of oil of the entire world would scarcely 
be adequate to meet the consumption of fuel by the railway 
corporations of America, to say nothing of the stationary 
plants. 

(6) Most of the burners make a roaring noise which is 
objectionable in many places. 

(7) The heating-surfaces of the boiler are apt to become 
coated with a deposit which is the residue of incombustible 
matter in the oil. 

(8) The difificulty which is caused by a tendency of the 
oil to creep past stop-valves and make a leakage which is 
annoying and sometimes dangerous. 

(9) The necessity for an auxiliary apparatus either to start 
the oil-fire, or to maintain it, or both. If the oil is vaporized 
and carried by air, an air-pump must be driven by the boiler 
itself to supply compressed air, and in starting this must be 
furnished by an independent apparatus. If steam induces the 
current of oil, an auxiliary or donkey boiler must be started 
by coal to give the necessary pressure. With respect to the 
use of steam or air, the latter offers the disadvantage of extra 
machinery, but has the advantage of supplying a material 
which is a supporter of combustion. The air, on the other 
hand, is cool, while the steam is hot. 

It would seem, therefore, that oil-firing, while possessing 
many advantages, is not at present commercially practicable 
in most instances. 

300. Gas as Fuel. — Where natural gas can be brought to 
the boiler-furnace to be burned as fuel, or where the manu- 
facture of combustible gas is incidental to the industrial 
process, as in iron-making, or where gas can be furnished at a 
low rate by direct manufacture, it offers many of the same 
advantages in boiler-firing as are offered by oil, and it avoids 
all the disadvantages. 

The objection to firing all boilers by gas is, first, that the 
radiant heat of the burning fuel in the fire-box is lost to the 
boiler if the gas is made outside or in a separate process. 
The second difficulty is that most boiler-settings are not 



THE BOILER-FURNACE AS THE ORIGIN OF POWER. 5/1 

adapted for gas-firing by reason of the necessity for keeping 
the temperature of the gases up to the point of ignition so as 
to secure complete combustion, while the business of the 
boiler is to cool them down as quickly and as far as possible 
so as to withdraw their heat and store it in the water. 

A fuel-gas with low illuminating power can be made for 
boiler purposes either in a gas-producer which shall supply 
all gas needed from a central point, or each boiler or battery 
of boilers may have its own small producer, or each boiler 
may be made into a gas-producer which shall burn the gas 
under the boiler proper as it is formed in the fire-box. This 
latter method underlies many forms of setting which have 
been found successful for the burning of the soft and the 
gaseous coals. Fig. 469 shows a boiler-setting of this general 
type, in which the fire-box is a fire-brick chamber in front of 
the boiler itself, and the gases distilled in the fire-box are 
heated by it to an ignition-point and are then discharged into 
the boiler-setting proper to impart their heat through the 
boiler. A condition of almost this same sort is present when 
sawdust is to be burned, or any similar material whose fine 
state of division makes it form combustible gas with great 
rapidity. The best results are obtained by withdrawing the 
heating-surface entirely from the space where gas is produced 
or evolved. The blast-furnace furnishes carbonic-oxide gas 
for fuel, and if enough is supplied it will be burned under the 
boilers. 

The burner for gas is either an annular arrangement of 
pipes like an Argand burner, so that the gases and air shall be 
intimately mixed, or else the gas comes up through perfora- 
tions in a fire-brick grate-surface and meets the air for com- 
bustion on the top. Great care must be taken in gas-firing to 
guard against the accumulations of an explosive mixture of 
gas and air, which may take fire and by its expansion of 
volume do great injury to the setting or to the boiler itself. 

The installation of steam-boilers over the furnace for heat- 
ing or puddling steel or iron belongs to the subject of gas-fired 
boilers, since it is desirable that the products of combustion 



572 MECHANICAL ENGINEERING OF POWER PLANTS. 




THE BOILER-FURNACE AS THE ORIGIN OF POWER. 573 

in heating or puddling should not contain oxygen in the 
heating-furnace, and are therefore usually in a combustible 
condition when they leave the furnace, so that they can be 
ignited within the boiler-setting and impart their heat by 
radiation as well as by contact. The condition of gaseous 
firing, that the gases shall not be extinguished by having their 
temperature lowered, adapts the two-flue boiler for steam- 
making under these circumstances (par. 233). 

301. Smoke-prevention. — While the foregoing discussions 
have plainly indicated that the condition of smokeless firing 
for boilers is that the combustible gas given off by the fuel 
shall be kept at a high temperature, and shall have time and 
room enough in the setting to unite with oxygen and burn 
completely, it is not easy to secure these conditions and at 
the same time maintain an economical transfer of heat to the 
boiler and to the water. The rapid and efficient transfer of 
heat by radiation makes it desirable that the products of com- 
bustion leaving the boiler-furnace shall be full of glowing or 
incandescent carbon which shall give a long flame, and to 
secure the combustion of this gas at the end of its transfer is 
not an easy thing to do. Hence where smoky fuels have 
been the usual ones a large number of methods have been 
attempted to secure smokelessness by preventing the pres- 
ence of these glowing particles, or by having the combustion 
complete in the fire-box proper and not beyond it. The 
various methods for smoke-prevention have been grouped 
under the following heads: 

(i) The supply of excess of air by steam-jets, inducing 
currents which they warm, and supplying excess of warm air 
above the fire and behind the bridge-wall. The difBculty 
with these has been that after distillation of the gas is com- 
pleted following a charge of fresh fuel thrown on the fire, this 
excess of air is not needed, and the products of combustion 
are cooled by the diluting oxygen. Attempts have been 
made to correct this by graduating the supply of fresh air by 
chronometric or other appliances, so that the excess should 



574 MECHANICAL ENGINEERING OF POWER PLANTS. 

be cut off after such an interval as is usually needed for the 
first distillation of gas. 

(2) By the coking methods of firing. By these plans a 
large dead-plate was used (par. 268) so that the gases should 
be distilled off from the fresh fuel before its combustion was 
really begun on the grate-surface proper, and when the coking 
was complete only fixed carbon remained to burn on the grate- 
surface proper when pushed back. The gas distilled from 
the fuel on the dead-plate passed over the hot fire and was so 
warmed that it was ready to combine and burn. Alternate 
firing of the two sides of the furnace, or the use of two furnaces 
delivering into a common combustion-chamber, which were 
fired alternately, belong to this same class. 

(3) The methods belonging to the principles of mechanical 
stoking (pars. 271 to 275) are smoke-preventing methods in 
that each part of the fire always remains in the same condi- 
tion, and the fresh coal which distils off gas is received in the 
coolest part of the grate, and passes to the hotter sections 
only after the volatile matter has been distilled off and 
burned in passing over those hottest portions. 

(4) Gas- and oil-firing are smoke-preventing methods, 
since when properly done the combustion ought to be com- 
plete, and no carbon should pass out of the setting except in 
the form of carbonic acid. It is to this group that those 
settings belong in which the actual combustion of the fuel con- 
taining volatile matter is done in a separate furnace and away 
from contact with the boiler (par. 300). This makes a rela- 
tively smokeless and efficient principle, and will answer with 
coals which cannot be economically burned in any other way.' 

(5) The down-draft furnace appears to be one of the most 
successful appliances for smoke-prevention with smoky coals. 
As satisfactorily applied it involves the use of two sets of 
grate-bars, one over the other, so arranged that the draft 
passes downwards through the upper and lower sets of bars, or 
else passes downwards through the upper and upwards through 
the lower. Each set has its own fuel, but the intention is 
that the gases shall be distilled off from the fresh fuel on the 



i 



THE BOILER-FURNACE AS THE ORIGIN OF POWER. 575 




57^ MECHANICAL ENGINEEKING OF POWER PLANTS^ 







THE BOILER-FURNACE AS THE ORIGIN OF POWER. 5// 

Upper grate, and shall be drawn downwards to mix with the 
hot products escaping from the lower where the solid carbon 
is burning. By this the temperature of ignition is maintained 
for the distilled gas, so that it shall burn with the abundant 
supply of warm air admitted for this purpose. Figs. 470 and 
471 show boiler-settings of this type. 

(6) The use of fire-brick or similar refractory material in 
the combustion-chamber, This becomes hot by the impact 
of flame and gas, and keeps the temperature of the gas up to 
ignition. It imparts some of its heat to the boiler by radia- 
tion after it is once brought up to full heat. 

(7) Preheating of the air-supply by hollow walls or flue- 
boxes which the hot gases surround while the fresh air flows 
within them. 

The objections to most of the smoke-prevention devices 
have been that the introduction of such appliances diminishes 
either the economy or the capacity of the plant as compared 
to what it was when the chimneys were allowed to smoke. 
The excess of air, diluting the products of combustion explains 
a loss of economy and capacity, and the superior efficiency of 
the yellow flame, as compared with the colorless flame of per- 
fect combustion, is also responsible in part for this result. 
The losses seem to be about 12 per cent of power or from 7 
to 13 per cent of economy. 

The term smoke-consumption or smoke-burning is an im- 
proper one, since a true smoke consists of a current of hot 
gases in which particles of carbon in the form of true lamp- 
black are carried. Such lamp-black once made is incombusti- 
ble and cannot be burned. The products of combustion are 
often colored brown by the presence of tarry or similar com- 
bustible matters, and these will ignite if the temperature be 
made hot enough. It is possible to prevent the appearance 
of smoke by catching it in water through which the products 
of combustion pass, and in which the carbon is thrown down. 



CHAPTER XXVI. 
BOILER ACCESSORIES AND APPLIANCES. 

302. Introductory. — The typical boiler, whether inter-. 
nally or externally fired, requires for its safe handling and 
proper management certain appliances and apparatus hav- 
ing to do with the observation of the transfer of heat, and 
the supply of water to be made into steam, and also as means 
-for securing its safety against accident. Such accessories are 
the gauges for water and for steam, the feed apparatus and 
heaters, the safety-valve, and the blow-off connections. 

303. Steam-gauge. — It is important that the fireman in 
charge of a boiler should know whether the fire is supplying 
heat-energy to the water faster than it' is being withdrawn in 
the form of steam, or slower, or just at the proper rate. The 
most convenient indications of the heat-reactions are given by 
an appliance which shall record the pressure in the boiler, 
since if the pressure is rising, heat is being stored by the 
water, and if the pressure is failing, heat is being given off 
faster than it is being supplied. This strictly and properly 
is the principal function of the steam-gauge. A secondary 
but sometimes very important function is to indicate whether 
the pressure and the heat-supply are rising so rapidly as to 
endanger the structure from excess of internal pressure. 

The first and simplest form of steam-gauge is a U type or 
manometer. The size which this appliance is to receive with 
high pressure precludes its use as a pressure-gauge, although 
it remains the standard for all of its more convenient substi- 
tutes. It has been found most convenient to replace the 
weight of the mercury-column by a spring which shall undergo 

578 



BOILER ACCESSORIES AND APPLIANCES. 



579 



a known deformation for each pressure, and which shall indi- 
cate its deformation by the movement of a needle over a dial. 
Such spring may either be a flat disk or diagram, Fig. 472, 
or it may be a hollow brass or steel tube which is bent into 
an arc of a circle, and the sides permitted to come together 
by this bending, so that the section of the tube is that of a 
very much flattened oval. When pressure is admitted on the 
inside of this tube the parallel sides tend to separate, and in 
separating they must increase the radius of curvature with 
which the tube was bent within the circle. The tendency to 




Fig. 472. 

straighten out by internal pressure, can be indicated by a 
multiplying gearing which shall cause an indicating-needle to 
traverse an arc. Fig. 473 shows the ordinary Bourdon gauge 
with flattened tube availing of this principle. Pressures below 
that of the atmosphere can be observed by similar appliances. 
The aneroid barometer is a vacuum-gauge. 

Fig. 474 shows a form of Bourdon spring in which the two 
arms have been shortened so as to prevent their shaking dis- 



580 MECHANICAL ENGINEERING OF POWER PLANTS. 

agreeably when exposed to the jarring in locomotive service. 
Sensitiveness or a considerable motion of the needle is 
secured by a double connection to the multiplying device. 



I 




Fig. 473. 

This arrangement is also of advantage for use in gauges which 
are to be exposed in portable boilers to temperatures below 
freezing. The two arms can be drained of the water which. 




FiG. 474. 

they will contain from condensation, whereas the form of Fig. 
473 will always hold the watc that had once entered it. It 
is usual to secure the separation of hot steam from the gauge- 




BOILER ACCESSORIES AND APPLIANCES. 581 

spring by an intervening water-column, for which provision is 
made by connecting the gauge to the boiler through a U tube, 
which will naake a siphon (Fig. 477). Fig. 475 
shows a device which produces the same effect 
as a water-seal. Provision, however, should be 
made for draining this siphon both for cleansing 
indoors and to prevent freezing without. 
The defects of such spring-gauges are: 
(i) The spring loses its original resilience by 
use and heat. If this is due to a permanent 
change in the structure of the material, the y\q. 475. 
gauge is useless. 

(2) Rust and improper treatment may cause the friction 
of the needle mechanism to prevent the recording of the full 
pressure against the spring. 

(3) The needle may slip so as to change its relation to the 
spring, which will cause the gauge to record permanently 
above or below its proper pressure. 

304. Standardizing or Calibration of Steam-gauges. — 
To ascertain the accuracy of a gauge it is to be compared with 
a standard. It is usual to compare it in practice with a test- 
gauge, which is one kept specially for this purpose and not 
exposed to the conditions of service. The test-gauge, how- 
ever, requires to be itself standardized, and for this purpose 
three methods are usual. The first is to connect the gauge 
which is to be tested upon a pipe or similar apparatus within 
which hydraulic pressure can be admitted to come also upon 
a valve closing an opening which is made exactly one square 
inch of area. By loading this valve with known weights, and 
observing the pressure recorded by the gauge when the water- 
pressure lifts the valve and weights, the gauge is calibrated. 
This can also be done with a piston which can be loaded with 
known weights moving without friction, or with a minimum 
friction, in a cylinder. 

The ultimate standard is the mercury-column. The gauge 
to be tested is connected on the same pipe which opens into 
the short leg of the mercury-column, and the pressure re- 



582 MECHANICAL ENGINEERING OF POWER PLANTS, 

corded :n the gauge when the mercury in the long leg stands 
at the heights which correspond to the real pressure indicates 
its error or its truth. 

305. Recording-gauges. — It is convenient to have a con- 
tinuous record of the variations of pressure in the boiler or in 
the other appliances in which pressure is to be observed. It is 
very simple to connect the spring or piston mechanism of the 
gauge or testing appliance to a link carrying a pencil-point 
which shall move in one direction by variation of pressure over 
a piece of paper which is made to travel in a direction at right 
angles at a known rate by means of a clock. The pencil-point 
traces a line as the pressure directs, and the intensity of that 
pressure is measured by the vertical ordinates on the diagram, 
while the time at which it occurred can be found by a hori- 
zontal measurement. 

306. Water-gauges. — It will be apparent that a device 
must be furnished to a boiler such that the operator in charge 
can see whether the water is being supplied to it at the same 
rate that steam is being withdrawn from it, and regulate the 
supply of feed-water accordingly. As with the steam-gauge, 
a secondary use of the water-gauge device will be to enable 
the attendant to see whether the quantity of water, or the 
level of water, in the boiler is falling so low as to expose heat- 
ing surfaces to the action of gas or flame without water on the 
other side, and also whether the water-level is rising to a point 
at which the priming or mechanical entrainment of water 
would be feared. The danger from low water-level in the 
boiler, whereby overheating is caused, would be that any or 
all of three injuries would follow. First, a general over- 
heating would cause a corrosion or wasting of the iron by 
oxidation. Second, if there were any lack of homogeneity in 
the plate from cinder or defective welds, a blister would be 
caused; and third, when the overheated plate was cooled 
suddenly by filling the boiler with cool water the reduction of 
temperature would cause a sudden shrinking which, if not 
general and easily yielded to, might strain some joint of the 
boiler beyond its point of resistance when the boiler was 



BOILER ACCESSORIES AND APPLIANCES 583 

already under considerable strain from the internal pressure. 
It is this last danger which makes low water so often a con- 
tributing cause to a boiler-disaster. 

307. The Glass Water-gauge and Column-pipe. — The 
simplest form of water-gauge is a glass tube about a foot long 
or a little over, which is connected by proper fittings so that 
its bottom should be below the lowest water-line, and its top 
above the highest (Fig. 476). These fittings are screwed into 
the head of the boiler directly in boilers which are not set in 
brick, and the water will stand in the glass tube at the same 
height that it stands behind the head of the boiler. A simple 
inspection by eye is all that is necessary to see whether the 
water-line is above or below the normal. In boilers set in 
brick, where the head is not exposed, the gauge-glass will be 
carried upon an independent vessel which will be connected 
by proper pipes above and below the water-line respectively. 
This fixture is called a column-pipe (Fig. 477), and the water 
in it should stand at the same level as that in the boiler, and 
therefore make the gauge-glass show the water-level in all 
three vessels. Care must be taken in connecting the column- 
pipe that it shall be easily cleansed of deposit or other material 
which might clog it, and prevent its giving the same indica- 
tions of level as are correct for the boiler itself. 

The advantages of the gauge-glass are its simplicity, its 
cheapness, and that it is easily observed. 

The objections to it are: 

(i) Its fragility. It may be broken by accidental blows in 
spite of the brass-wire guards ml shown in Fig. 476 to prevent 
this accident. Furthermore, it is liable to break from a defec- 
tive alignment of the two fixtures cramping the glass and 
causing it to crack, and also from a deterioration which the 
glass undergoes in service, particularly with waters contain- 
ing any alkali. In locomotive practice the jarring tends to 
break the glass, and in confined spaces it is specially liable to 
accidental injury. When the glass breaks under pressure it 
will be apparent that two very powerful jets of hot water in 
one direction and of steam in another are thrown out from the 



584 MECHANICAL ENGINEERING OF POWER PLANTS. 




TOP OF UPPER 

oworTliflK. 



DMKCER SPACE 
fir BOILER. 



AiRcaetG 




Fig. 476. 



Fig. 477. 



BOILER ACCESSORIES AND APPLIANCES. 



585 



-fixtures, and under high pressure will fill the room instantly 
Avith hot and irrespirable steam. To prevent this difficulty a 
form of gauge-glass fixture has been devised in which the two 
attachments have an automatic valve opening inwards, and 




held in that position by a spring (Fig. 478) or by gravity 
(Fig. 479). When there is equal pressure on both sides of 
the valve the opening is clear into the glass-tube. When the 
tube breaks, the outrush of steam and water will close the 



586 MECHANICAL ENGINEERING OF POWER PLANTS. 



valves against the spring or gravity and thus automatically 
shut off the broken tube. Fig. 479 shows this device with a 
ball as the valve to be closed when breakage occurs. The 
pin on the end of the spindle of the hand-valve (Fig. 478) 
forces the automatic valve away and opens the connection 
through the glass when the spindle is withdrawn. The spin- 
dle should be withdrawn slowly, so that the pressure may^ 
equalize in the tube without drawing the valve to its seat. 

(2) The gauge-glass may give false indications. This may 
happen because the somewhat tortuous passage in the lower 
fixture has become stopped with scale. This can be guarded 

against only by frequent opening 
of the blow-cock at the bottom 
of the fixture, so as to wash it 
out and be sure that the passage 
to it is free. The indication may 
be deceptive because the lower 
valve is closed, preventing the 
water from descending in the 
glass when it descends in the 
boiler. This is best guarded 
against by making the valves of 
the fixtures to be cocks operated 
with a handle whose position 
indicates whether the valve is 
open or closed (Fig. 479). The 
third objection is the invisibility 
of the water in the glass when the 
water is clean. This can be ob- 
viated by having a colored strip 
made in the glass at the back 
which will be visible through the 
steam above the water, but which 
will be made invisible by diffrac- 
tion caused by the water within 
Fig. 479. ^j^g glass. The water usually is 

slightly colored, and it can be detected with care even if it 




BOILER ACCESSORIES AND APPLIANCES, 58/ 

is clean. The freedom of the connections between the gauge- 
glass and the boiler can also be insured when the boiler is 
steaming by observing the motion which the operation of 
steaming always causes in the water in the boiler from the 
presence of waves. Fig. 477 shows a standard water-column 
with the connections for cleansing at the bottom. 

308. The Gauge-cocks. — By reason of the difficulties 
attaching to the gauge-glass, another form of water-gauge is 
usual without the glass or in addition to it. This involves 
the making of three or four openings into the boiler which 
can be opened by valves, and through which openings a sam- 
ple can be taken from the level into which the openings are 
made. Such valves are called gauge-cocks or try-cocks, and 
will be fastened by screwing into the head of the internally- 
fired boiler, or into the column-pipe of the brick-set boiler. It 
will be apparent from Fig. 477 that if there are three of these 
cocks, the middle one should be at the normal water-level, 
the upper one above it, and the lower one below it. If the 
cock be opened above the water-line, it will permit dry steam 
to flow out, and its quality will be revealed to the eye and to 
the ear. The passage through the small opening will tend to 
superheat the steam, so that it will be an invisible gas for an 
inch or two from the nozzle, and will give a sound like the 
escape of a true gas. From the lowest cock water will be 
drawn, if it is below the water-level, but this water on reach- 
ing atmospheric pressure at the outlet will at once become 
saturated steam, which will be a white cloud from the very 
outlet of the valve, and will reveal itself to the ear by the dif- 
ference in sound of the escape of water as compared with the 
sound of escaping gas or air. The middle cock, when the 
water-level is practically opposite its opening, will withdraw 
both steam and water, which will make the characteristic 
sputtering noise of air and water escaping through an outlet. 
The appearance to the eye will be the same as from the lower 
cock, since the water is the visible thing. Large boilers often 
have four cocks. 

These gauge-cocks require to be opened by hand, and 



588 MECHANICAL ENGINEERING OF POWER PLANTS. 




Fig. 480. 





Fig. 481. 



BOILER ACCESSORIES AND APPLIANCES. 589 

therefore must be modified for boilers whose water-level is 
higher than convenient reach. Different forms of try-cocks 
have been introduced, operating either by a weight which has 
to be lifted to open them, or else they are made like cock- 
valves which can be easily turned by an extension which comes 
down to convenient reach. Figs. 480 and 481 show types of 
gauge-cocks. 

309. Float Water-gauges. — It has been sought for many 
years to find a satisfactory method of indicating the water-level 
by means of floats within the boiler whose position should 
cause the motion of a convenient indicator without. Some 
very early boilers had water-gauges of this class. The objec- 
tion to them is the friction, which is a variable quantity and 
which acts upon the means used to transmit the motion of the 
float to the indicator outside the boiler. The float is apt to- 
catch and be held by such friction, and fail to indicate the 
real changes in water-level. The other difficulty is that no 
float material has been found which does not ultimately 
become affected by heat and pressure, so as to absorb water 
from the water in which it stands, and thus become either 
partly or entirely filled. It seems to be a general idea that 
it is not safe to put dependence upon float-gauges for these 
reasons. 

310. Low-water Alarms. — It is quite possible, however, to 
use the float as a means of giving warning that the level in the 
boiler has been allowed to fall too low. This use is justified 
from the fact that they are not depended on, or should not 
be, for the normal working of the boiler, but are present as a 
safeguard if they fulfil their purpose in emergency. The 
usual plan is to allow these floats to control a valve where 
steam shall be admitted to a whistle. The normal rise and 
fall of the float within the limits of safe working is without 
effect on the whistle-valve, but it opens it if the float is too 
high or too low. A similar device can be arranged depending; 
on the difference of expansion of metals in steam or in water. 
When a spindle is surrounded with water it is short enough 
to hold a valve shut, but when the water falls below the 



590 MECHANICAL ENGINEERING OF POWER PLANTS. 

opening into the tube within which that spindle stands, the 
expansion of the spindle will open the valve. 

311. Fusible or Safety Plugs. — As an additional safeguard 
to prevent injury from low water it has been the custom of 
many engineers and of some state legislation to demand that 
a plug shall be inserted into the boiler, at or near the danger- 
ous low-water line, made of Banca tin or of some of the cad- 
mium alloys, which have a relatively low fusing-point. When 
the disk or plug of such fusible metal is covered with water the 
heat is transferred so rapidly that it should not melt. When the 
water leaves the plug, the lowered specific heat of steam pre- 
vents the rapid withdrawal of heat, whereupon the plug melts, 
and steam blows out through the opening to give warning of 
trouble. Fig. 482 shows a construction of such fusible plug 



1 




Fig. 482. 

in which a brass shell is fitted with a core or disk of fusible 
metal. The objection to such fusible plugs is, first, that the 
melting-point of most of these alloys changes with time and 
is not always certain. Secondly, when covered with a crust 
of boiler-scale they may not be properly cooled by the water, 
and fuse when everything in the boiler is normal. On the 
other hand, they sometimes fail to act either from the first 
difTficulty or from some unknown cause, and in any event, 
when blown out, it is annoying to replace them. The loca- 
tion of such fusible plug in a tubular boiler is shown in Fig. 

A^6, 



BOILER ACCESSORIES AND APPLIANCES. 59 1 

The fusible-plug alloy has been applied as a safety or low- 
water alarm by inserting a disk or diaphragm of metal of this 
fusible quality in a pipe which admits steam to an alarm- 
whistle. When the pipe is sealed by the boiler-water, the 
plug does not become hot enough to melt. When the fall of 
the water-level permits the water to flow out of the tube, steam 
replaces it and has a sufficient temperature to melt the plug 
and blow the whistle. 

312. Introduction of the Feed-water. — The water to be 
•evaporated by the boiler is fed to it as a rule cooler than the 
water within the boiler. It should therefore be introduced at 
such a point as to favor and not impede the currents of circu- 
lation and convection within the boiler; and furthermore, if it 
can be persuaded to deposit the solid matter which is con- 
tained in the feed-water immediately on entering the boiler, 
it is desirable to have regard to this in selecting the place at 
which the water shall enter. In sectional and most of the 
shell boilers this indicates that the water should commence to 
ilow within the boiler at or near the surface, and at the back 
of the boiler or where the heaviest water is descending. By 
having the feed-water enter at the surface there is also met 
less danger from the siphoning of the water in a boiler out 
through the feed-pipe either to another boiler or to waste, if 
anything is wrong with the check-valve which should prevent 
this action. Boilers may empty themselves through a feed- 
pipe which enters at the bottom; but where the feed-pipe is 
near the surface of the water, the water below its level can 
only get out by evaporation. This further produces less 
injury to the metal of the boiler near the feed-inlet from 
sudden change of temperature. 

It is more convenient, however, to have the valves control 
the flow of feed-water into the boiler at the front rather than 
at the back. This has given rise to a very prevalent practice 
■of carrying the feed-pipe through the front head, and along 
the length of the boiler to that point farthest from the fire at 
w^hich the water shall actually mix with the water in the boiler. 
This serves to bring this entering water up somewhat nearer 



592 MECHANICAL ENGINEERING OF POWER PLANTS. 

the temperature of the boiler-water before it strikes the shell- 
plates. This inner feed-pipe is sometimes perforated along" 
its length with the idea of causing the cold water to enter in 
fine streams rather than all at one place. The objection to 
the .interior pipe, and particularly to a perforated one, is its 
liability to become stopped up by matter precipitated from 
the water by heat. It appears in Figs. 456, 469, and many 
others. 

313. The Feed-pipe and Feed-valves. — The feed-water 
will be introduced into the boiler through a feed-pipe on which 
will be certain controlling valves. The pipe is very often 
made of copper by reason of its flexibility and ductility under 
the changes of temperature to which it is exposed, and because 
bends are easily made in it, and because the solid matter pre- 
cipitated from the water does not adhere to it. Iron pipe, 
which is often used in stationary practice, has the advantage 
of being cheap and that the fittings which are required are 
easily made and attached to it, which is not the case with the 
copper feed-pipes. The diameter of the pipe should be chosen 
j^^^^^^^^^^. fifst with respect to having, the velo- 

ij^^^^^^fcr"'""'^^\ city of the water through it not ex- 

j ^ ^^ M p ii "\ ceed 400 to 600 feet per minute of 

^^^^^^^^Ml i linear velocity. It is desirable also 

MJBBgl^^H^^^^^p that the feed-pipe should be large 

^^^^^^^ ^^^^^^ ' enough so that even if it should be- 

^^ come somewhat stopped up with 

scale, as has occurred in the example 

shown in Fig. 483, it may be possible to get the scale out, 

or to leave still space enough through which the water can 

be forced. 

Upon the feed-pipe will be the necessary valves. The 
first of these is one for controlling the flow of feed-water into 
the boiler in question if a number of boilers are supplied 
through a common pipe. This will be through a cock-valve, 
which is preferred in English practice, or a globe valve, which 
is more usual in American practice. The cock-valve is not 
liable to clogging from precipitated scale, which is a difificulty 



BOILER ACCESSORIES AND APPLIANCES. 593 

connected with the globe valve, but with modern forms of 
globe valves they are easier to keep tight than a taper plug. 
The latter also gives trouble sorqetimes by expansion, although 
the packed-stem plug-valves are not open to this difficulty. 
Close to the boiler where the feed-pipe enters it will be a 
check-valve. This is imperatively necessary where several 
boilers are connected to a common feed-pipe, but is desirable 
in every case. The check-valve lifts by excess of pressure on 
its lower side, as compared with the pressure in the boiler, 
which bears upon its upper side. Its object is to prevent 
water which has once gotten into the boiler from getting out 
again back into the feed-pipe. This serves to keep the scale 
out of the feed-pipe, to prevent siphoning of water from one 
boiler into another, and to prevent hot water from working 
back to the pump where it would be troublesome. These 
check-valves are made to work in horizontal or vertical pipes. 
The difficulty to which the}^ are liable is a tendency to leak 
through abrasion of their seats, or by being held off the seat 
wholly or in part by some solid matter in the feed-water 
which gets caught in the valve. All such check-valves have 
an opening to permit access to the valve for inspection and for 
repairs (regrinding of the seat, or renewal of the valve-face) 
(Figs. 484 and 485), and in order to permit this repair or 
inspection without emptying the boiler of pressure and of 
water it is desirable to interpose a cock-valve between the 
check-valve and the boiler, so that the latter can be cut off 
from the check-valve when it is to be inspected. 

314. The Supply of Feed-water to the Boiler. — The 
pressure in the boiler is, as a rule, much higher than the 
pressure which prevails in the ordinary water-works system, 
and consequently special appliances are called for to get water 
into the boiler against the pressure which prevails in it. This 
motion of the water can be secured either by a pump or by 
an injector. There are two great methods of feeding by 
means of a pump. In one the feed-pump is driven by the 
main engine of the power plant, either directly from its 
mechanism, or indirectly from the machinery of transmission 



594 MECHANICAL ENGINEERING OF POWER PLANTS. 




Fig. 484. 





Fig. 485. 



BOILER ACCESSORIES AND APPLIANCES. 59$ 

through belting and gearing. This principle, however applied, 
has certain advantages and disadvantages. The advantages 
are that the feeding of water will be constant, and propor- 
tional to the consumption of steam. It is possible to control 
the supply of water so closely that the pump shall replace in 
the boiler at each stroke as much water as is withdrawn by 
the cylinder in the form of steam. It is the usual design of 
pumps of this class to have a capacity one and one quarter 
times the maximum evaporative capacity of the boiler, and 
regulate within and below this limit by partly closing the valve 
which supplies the pump on its suction side. The barrel is 
therefore not quite filled at each stroke when the pump is not 
running at its full capacity. The second advantage of this 
attached s\^stem is that the power required to feed the boilers 
is furnished by the main or principal cylinder, and is probably 
therefore more cheaply obtained than if a smaller special 
pump is run for this purpose. The objection to this principle 
is that in order to feed the boiler the entire engine or trans- 
mission machinery must be run. 

The detached system or donkey feed-pump method is to 
pump by means of a special steam-engine with its own cyl- 
inder. This avoids the last difficulty, but the weight of steam 
used for feeding in this way is probably greater than by the 
other system. It is most frequent to have both systems, 
particularly in an engine of slow rotative speed. The advan- 
tages of economy and continuous feeding are secured when 
the engine is running, and the donkey pump can be used 
when the main engine is still. 

315. The Fly-wheel Pump. — The fly-wheel pump is a 
form of donkey-pump which has been much used for boiler- 
feeding. It is a steam-engine with all the usual mechanism, 
but with a pump-cylinder on the prolongation of the piston- 
rod (see Fig. 4). The advantages which it offers are: 

(i) It is simple and positive in its action 

(2) This adapts it for use where but unskilled labor is to 
be had. 



59^ MECHANICAL ENGINEERING OF POWER PLANTS. 

(3) It secures economy of steam-consumption by its ability 
to work the steam expansiv^ely. 

(4) Its stroke is a positive length determined by the crank, 
and if necessary it can be worked as a hand-pump by turning 
the fly-wheel. 

The objections to the fly-wheel pump are: 

(5) It cannot be run slowly without danger of stopping on 
its dead-centres. 

(6) It cannot be conveniently controlled therefore by 
valves upon the delivery-pipe from it. 

(7) The objection which has been urged against fly-wheel 
pumps that they accelerate the flow^ of the water through the 
pump-cy]inder as the velocity of the piston is controlled by 
that of the crank, has no significance with the relatively small 
masses of water which these pumps are required to handle. 

316. Direct-^acting Pump. — The direct-acting pump dif- 
fers from the fly-wheel pump by having no crank, shaft, or 
revolving wheel, but simply the steam- piston on one end of a 
piston-rod, and the pump-piston or plunger at the other (Fig. 
486). Since there is no stored energy or velocity in a revolv- 
ing or moving mass to carry the motion past the end of the 
stroke and cause the engine to reverse, this result must be 
obtained by having the valves thrown by steam, as discussed 
in par. 113. The main piston turns steam on to the valve of 
the auxiliary steam-engine, whereby the valve of the main 
engine is moved and the principal steam-ports opened. If 
this auxiliary engine is also a pumping-engine, the pump 
becomes what is called a duplex pump. 

The advantages of a direct-acting or non-fly-wheel pump 
are: 

(i) The velocity of the delivery is proportional to the re- 
sistance offered by the water. Hence it is possible to control 
the feed-pump of the boiler when of this class by the opening 
and closing of valves upon the delivery. When the resistance 
to the delivery exceeds the forw^ard effect of the steam-pres- 
sure the pump stops. The forward or feeding force is secured 



BOILER ACCESSORIES AND APPLIANCES. 



597 



by making the area of the steam end of the pump three or 
four times the area of the water end. 

(2) The pump has no centres, but will start from rest as 
soon as steam is turned on to it. This property is the result 




of the steam-thrown valve, because the main valve is open at 
one end of the cylinder until reversed and opened wide at the 
other end. 

(3) The pump can be run as slowly as suits the conven- 
ience or the requirements of the feeding. 



59^ MECHANICAL ENGINEERING OF POWER PLANTS, 

(4) The velocity of flow is not accelerated by the connec- 
tion of the piston to revolving mechanism. 

The objections to the non-fly-wheel pump are: 

(5) That the steam-thrown valve does not encourage 
expansive working, nor at ordinary speeds can it be secured 
when there is no fly-wheel to store up excess of work at one 
part of the stroke to give it out at the second part. In large 
water-working pumping-engines this has been secured by 
devices which are not considered worth while for feed-pumps. 

(6) The stroke is not positive in length, as there is nothing 
to compel it to be so. 

(7) This compels an excessive clearance-volume in the 
steam-cylinder in order to guard against the piston fetching 
up against the head when running at high speed. 

(8) The operation of the auxiliary engine and main valve 
being caused by steam, its operation is not always obvious, 
and this lends an appearance of complexity and mystery to 
their operation. 

The advantages where intelligent labor is to be had which 
belong to the slow running and easy control of the direct- 
acting pump have made it a very popular form for boiler- 
feeding. The fly-wheel type remains in general preference in 
Western river-boat practice and for fire-engines. 

It is not desirable to control a direct-acting pump by a 
valve on the suction, since the barrel of the pump should be 
perfectly filled at each stroke. Otherwise, when the pump 
reverses, part of the stroke will be made against little or no 
resistance, and as there is no controlling mechanism of crank 
and revolving shaft, a serious jar will occur when the pump- 
piston encounters solid water after part of the stroke is com- 
pleted. 

For similar reasons when a pump is to handle hot water it 
should receive the water from a height caused by gravity, and 
not be compelled to lift it. The vaporization of the hot 
water under the reduced pressure caused by the sucking action 
of the pump will prevent the barrel from filling, entailing the 
same difficulty from jar. When pumping hot water, further-^ 



BOILER ACCESSORIES AND APPLIANCES, 



599 



more, the pump will require to be fitted either with metallic 
valves or hard rubber resistant to the action of heat. With 
cold water the ordinary soft-rubber valves closed by springs 
are cheap, convenient, and tight. 

317. The Injector. — The injector is a mechanical appli- 
ance for feeding the water into a boiler against the pressure 
therein, and using for this purpose steam from the boiler 
which is to be fed. This seems like a mechanical paradox, 
since the principle of differences in area exposed to pressure 
cannot be availed of as in the pump, but the principles of the 
conservation of energy and its transformation from one form 
into another are able to explain and justify its observed action. 

The injector consists of a hollow, somewhat tubular cast- 
ing, usually of brass, into which are made three openings. 
The first one {A, Fig. 487), which usually enters the top of 
the instrument, is for the delivery to it of hot, 
dry steam from the dome of the boiler or other 
convenient place. The second opening, B, is 
the inlet for the water to be fed, which is usu- 
ally delivered to it from below. The third 
will be the feed-outlet, HI, opening towards 
the boiler, through which the feed-water im- 
pelled by the steam will pass to overcome the 
pressure on the check-valve and enter the 
boiler. 

The injector depends also upon the prin- 
ciple whereby a current of steam at high vel- 
ocity will induce a current of air to flow with it, 
so that by this action the air above the water 
in the supply-pipe to the injector will be rare 
fied and removed, permitting atmospheric 
pressure unbalanced in the water-pipe to force 
the water up through the steam-nozzle, and Fig. 487. 
thus make the instrument a lifting as well as a forcing appli- 
ance. When the steam from the boiler meets the water 
through the supply-pipe, the energy resident in the steam 
remains in the drops of water which result from the conden- 




600 MECHANICAL ENGINEERING OF POWER PLANTS. 

sation of that steam when it meets the water. These rapidly 
moving masses of water carry with them the excess of water 
supph'ed, and the rapid flow of the weight of water thus set in 
motion produces a continuous impact on the underside of the 
check-valve which the static pressure on its upper side is un- 
able to withstand. The valve is therefore lifted off its seat 
against the pressure in the boiler sufficiently to allow the mov- 
ing current of water to enter the boiler in a continuous warm 
stream. 

When the injector has to be a lifting injector, there will be 
a fourth outlet to it through which steam will be blown to 
waste during the few seconds necessary to exhaust the air in 
the pipe supplying cold water {G in Fig. 487). As soon as the 
steam passing out of the waste changes to water, it indicates 
that the lifting operation is completed and the waste can be 
closed, whereupon the instrument will feed to the boiler. 

318. The Handling of the Injector. — The operation of 
the injector as a boiler-feeding apparatus will be generally as 
follows : 

The waste-valve being open, steam is turned on either by 
an independent valve, or by a special valve of the injector. 
This steam will appear at the waste, and will blow through it 
until water is caught by the principle of induced currents, 
when the water will condense the steam and water will appear 
at the waste. The waste is then closed and more steam 
admitted to furnish the necessary energy to displace the check- 
valve. The amount of water delivered to the boiler will be 
determined by the amount of steam furnished. In some 
forms the lifting function is separated from the forcing func- 
tion, and is controlled by separate valves. In others the flow 
of combined steam and water through a primary set of 
nozzles is made to induce the flow of further water through a 
secondary, usually a parallel, set of nozzles. These instru- 
ments are usually called inspirators. The ejector is a form of 
injector in which, by enlarging the delivery-outlet so as to 
reduce the velocity at that point, the instrument obtains a 
capacity for handling larger weights of water, but against lower 



BOILER ACCESSORIES AND APPLIANCES. 



60 1 



resistance. High velocity of delivery is necessary to over- 
come great pressures. 

The modern forms of the injector are arranged to be oper- 
ated with one lever which is either so connected to the waste 
and the controlling inlet that they are operated in succession 




Ftg. 488. 



START 



BOILeR 




Fig. 489. 

as the lever is moved, or a partial motion of the lever opens 
the waste, while a complete motion closes it. This improve- 
ment not only simplifies the operation of the injector but 
makes it possible to locate it in places where it must be oper- 
ated by means of a rod (Figs. 488 and 489). 



602 MECHANICAL ENGINEERING OF POWER PLANTS. 

319. Advantages and Disadvantages of the Injector.— 

The injector as a donkey or independent boiler-feeding appli-^ 
ance offers the following advantages besides those which 
attach to the principle of feeding independently of the prin- 
cipal engine: 

(i) It is cheap. 

(2) It is compact so as to occupy but little space in pro- 
portion to its capacity as a machine for moving water. 

(3) It has no moving parts like piston, rods, etc., so that 
it has no running cost for repairs, but only that caused by the 
steam which it uses. 

(4) It delivers the water hot to the boiler. 

(5) It has no exhaust-steam to be disposed of, but carries 
its own exhaust-steam back into the boiler. 

These advantages of the injector have been of critical sig- 
nificance in fitting it for use in locomotives, where it is prac- 
tically universal. 

The objections to it are: 

(6) It stops working with variations in pressure of the 
steam, or will not start ivith a pressure less than that for 
which it has been designed. This is not true of all forms, but 
of those in which, as their feeding progresses, the pressure 
falls sufificiently to interfere with the working relation between 
the energy of the moving steam and the resistance offered at 
the check-valve. 

(7) Many forms when stopped in this way, so that the 
steam fails to be condensed by the water, get hot under these 
conditions and cannot be started without being thoroughly 
cooled. 

(8) The water to be fed cannot be much over 100° Fahr. 
in temperature. The instrument depends upon condensation 
for part of its action, and where the water is too hot to con- 
dense the steam it will refuse to work. 

The injector, by reason of the mechanical principle that a 
mass of water is only put in motion by bringing to bear upon 
it a mass of steam properly related to it, uses about as much 
steam in the operation of feeding as a pump, so that its 



BOILER ACCESSORIES AND APPLIANCES. 



605 



economy does not result from this cause. It derives its 
advantage from delivering warmed water without a preheating 
appliance or feed-water heater. 

320. The Economy of Preheating the Feed-water. — 
It has already been discussed in Chapter XXVI that the 
function of the coal is to heat the water from the temperature 
of the feed-water to that of the steam, and then to make steam 
of that water. If some of this heating can be done by heat 
which would otherwise be wasted, so much less coal is required 




Fig. 490. 

to be burned under the boiler. The calculation of the gain 
from preheating is not difficult (see notes). Two great types 
of feed-water heaters are to be met. The first are those in 
which the feed-water extracts from the steam rejected from 
the cylinder some of the heat which would otherwise be lost, 
and the other is the class which utilizes the heat which has 
escaped from the boiler-setting without being utilized in 
steam-making. The first class are called exhaust-steam 
heaters, the second class are called flue-heaters or econ- 
omizers. 

321. Exhaust-steam Heaters. — There are two great 
classes of exhaust-steam heaters. The first are known as 



604 MECHANICAL ENGINEERING OF POWER PLANTS. 

open heaters, in which the feed-water comes in direct contact 
with the exhaust-steam and withdraws its heat by direct con- 
densation. The other class are called closed heaters, in which 
the steam and water are in separate circuits of pipes or coils 

M 




Fig. 491. 
which have the steam on the outside and the water within, or 
the reverse. The open heaters are in some respects the most 
efficient, since the steam and water come together, and since 
sufficient heat is often imparted to the water to bring it to 



li 



BOILER ACCESSORIES AND APPLIANCES. 605 

that point at which it will precipitate the solid matter which 
it contains. This class of heaters have been called lime- 
catchers. Fig. 490 shows a form of this class of heater in 
which the water passes over the set of trays within the heater 
which are surrounded by the exhaust-steam. The hot water 
deposits its solid matter most rapidly in the thin films in 
which it escapes over the bottoms of the tra3^s, making; 
removal of such material complete, and the cleansing of the 
trays easy and rapid. Figs. 491 and 492 show types of the 
tube- or coil-heaters of the closed class. The tubes are apt 
to be of copper or brass, in order to be rapid conductors and 
are curved so as to yield easily to the condition of rapid ex- 
pansion and contraction to which they are exposed. It is 
convenient to pass the steam through the inside of small 
coils, because the only deposit in the small tubes is the lubric- 
ant, which is not so difficult to remove. The arched or flexible 
form given to the tube-plates and corrugation of the tubes 
also provide for these inequalities of expansion. 

Such steam-heaters will act partly as surface condensers if 
they have an abundance of surface, but care should be taken 
that the resistance offered to the exhaust should not impose 
a back pressure upon the engine-piston which should cost 
more coal to overcome than the saving of fuel caused by the 
heater. This is a matter of simple calculation when the back 
pressure is observed with the heater in action and out of action. 

322. Flue-heaters or Economizers. — The flue-heater is 
necessarily a closed heater, and consists of a coil of pipe 
through which the feed-water passes, while the outside of the 
coil is exposed to the heat of the gases in the chimney-flue. 
They are particularly advantageous when the temperature of 
the gases is unduly high upon leaving the setting, although it 
may fairly be urged that the boiler itself should have adequate 
heating-surface to cool the gases, without leaving this to be 
done by the economizer (Fig. 493). 

The advantages of the flue-heaters are that they heat 
the water to a high temperature, and higher than the exhaust- 
steam heaters when other things are equal. The exhaust- 



6o6 MECHANICAL ENGINEERING OF POWER PLANTS 



P) KSUJtFACE BLOW 



SURFACE\BLO\AI-DFF 




d^CO/IAMt-Ci tOi 




Fig. 492a!. 



BOILER ACCESSORIES AND APPLIANCES, 



607 



steam is apt to be at a temperature not much above boiling- 
point, whereas the flue gases 
may easily be hotter than 500° 
Fahr. 

The objections to them are: 

(i) That the difficulties from 
unequal expansion are very 
rgreat, and unless special care is 
taken both in manufacture and 
design these will cause leakage. 

(2) They are exposed to 
corrosion on the outside by the 
gases from most of the fuels, 
and particularly when a light 
covering of soot has coated the 
outside of the coil with an ab- 
sorbent covering which holds 
moisture and acids in contact 
with the metal. 

(3) When feed-water is not 
circulating through the coils so 
.as to keep them full of water, 
they will make steam which 
will escape through the check- 
valve into the boiler, leaving a 
part of the heater exposed to 
overheating. 

(4) They require to be 
cleansed from soot or tarry 
deposit by careful scraping in 
order to be kept efficient. The 
formation of scale within them 
will take place with waters hav- 
ing solid matter in them. Fig. 
493 shows the usual form of 
economizer with provision for 
external scraping, which becomes particularly easy with the 
vertical type. 




OWOFF 



Fig. 492(J 



6o8 MECHANICAL ENGINEERING OF POWER PLANTS 




BOILER ACCESSORIES AND APPLIANCES. 609 

In order that a feed-water heater may be efficient it 
requires to have an abundant contact-surface, and care should 
be taken, in selecting a heater, to secure this feature of its 
design. The standard proportion of an economizer is that 
there should be 9 feet of 4-inch pipe for each three horse- 
power in the boiler. 

Where the engine is a condensing engine the feed-water 
will be heated by the operation of condensation to a tempera- 
ture of about 100°. The feed-water heaters of the exhaust- 
steam class will heat the feed-water when well designed up to 
from 180° to 210°. Hence it would appear worth while even 
with a condensing engine to save the heat represented by 
heating the feed-water from 100° to 200° Fahr. in round num- 
bers, by interposing a heater between the cylinder and the 
condenser. 

323. Automatic Feeding Apparatus. — It has long been 
sought to arrange a mechanism which should be operated 
automatically, and as the level of the water in the boiler 
might vary, to have this change of level operate the feeding 
mechanism without human intervention. If automatic feed- 
ing in a reliable form could be combined with automatic 
stoking, the labor of the fire-room would cease to be manual 
and become supervisory only. 

It has been sought to obtain automatic feeding by several 
methods. They all make use of the direct-acting pump, and 
provide that the variation in water-level shall operate its 
steam-valve, so that the rise of the water-level above the 
normal shall shut off the pump, and a fall below shall turn 
on more steam and speed it up. This has been secured, first, 
by the expedient of having the steam-vaive operated by the 
pressure of a column of water against a flexible diaphragm. 
When the water-level was normal, or above it, the bottom of 
this column of water was sealed in the water and thus kept 
full by the steam-pressure. When the water fell below its 
opening into the water-space of the boiler, the column emptied 
its water into the boiler, and thus withdrew its pressure from 
the diaphragm, which yielded to an exterior weight and opened 



6lO MECHANICAL ENGINEERING OF POWER PLANTS, 

the valve. A second method has been to insert in a pipe a 
rod of some metal with a high coefficient of expansion. When 
the outlet from this pipe into the boiler was below the water- 
line, water was forced up into the tube, and its high specific 
heat and radiation kept the rod cool. When the pipe was 
emptied by the fall of the water-level in the boiler, steam 
replaced the water around the rod, caused it to lengthen, and 
turned on the valve. A third plan has been by means of 
floats whose rise and fall within the boiler transmitted motion 
outside through a proper stuffing-box to slow down or start 
up the pump. A fourth plan, which has been used since the 
development of the electric motor for pumping, has been to 
make the rise and fall of the water-level operate a float to 
throw out or in a switch or a resistance-coil, in the circuit 
driving the pump, whereby the action or speed of the pump 
should be made to vary. 

The fifth method has been to have the feed-pump operat- 
ing continuously, and to arrange that its suction should draw 
from the supply of fresh feed-water only when the water-level 
was below a certain point, determined as before by the seal 
of a pipe by the water in the boiler. When the water was 
above the opening of the sealed pipe the pump simply circu- 
lated the» boiler-water without drawing in a fresh supply. 

The idea of an automatic or magazine feed-pump is a very 
old one, and will be found applied to early boilers (Fig. 360), 
for which the feed was supplied from an elevated reservoir at 
such a height that the light pressure within the boiler could 
not balance the water-column, but water would flow in when, 
a valve was lifted by the water in the boiler through the opera- 
tion of a float. 

The objection to the automatic-feed principle as thus far 
applied has been that it is not entirely to be depended upon, 
or is not automatic in the true sense. 

324. Blow-off Valve. — The boiler requires to have a pipe 
connected to its lowest and coolest point to allow the boiler 
to be emptied for inspection and cleaning, as well as to be 
used for the removal of part of the contents of the boiler into 



BOILER ACCESSORIES AND APPLIANCES. 6l I 

the drainage system of the plant while at work, if this is 
desired. Such a pipe will be called the blow-off pipe, and 
will have in it, and as close to the boiler as convenient, the 
blow-ofT cock or valve. From its location at the lowest and 
coolest point the solid matter, mud, and precipitated salts 
will gather in its neighborhood, so that when opened with 
pressure on the boiler a rapid rush of the hot water out 
through the valve and pipe w^ill carry away some of the 
material of this sort. For this reason the blow-off valve is 
located in the mud-drum of boilers which have one. A gate or 
cock-valve is to be preferred for the blow-off valve, because it 
is not liable to become clogged from the precipitation of salts 
which may harden about it, and for this same reason also it is 
desirable that the pipe should be of generous size, so that it 
may easily free itself of the accumulations which may take 
place within it. It should rarely, even in a small boiler, be 
made less than 2 inches in diameter. In brick-set boilers, 
where the blow-off pipe must pass through the combustion- 
chamber, it is particularly liable to become burned out by 
the overheating to which it is liable if scale gets into it. It is 
for this reason quite customary to cover it with some incom- 
bustible and non-conducting material in that part of its length 
where it is exposed to flame and hot gas (see Figs. 367, 402, 
421, 431, 456, 459). 

In boilers using salt water the blow-off cock must also be 
used frequently in order to reduce the percentage of salty 
matter which is forced into the boiler with the feed-water, but 
cannot go out with steam. This opening of the blow-off valve 
is called blowing down, and permits the concentrated solution 
to be diluted by pumping in water to replace that which has 
blown to waste. 

325. The Safety-valve. — All modern boilers have attached 
to the steam-space a valve opening outwards and held upon 
its seat by a known force which is intended to balance the 
pressure upon its under side. It is called a safety-valve and 
is intended to act as a relief-valve, opening for the relief of 
pressure within the boiler when that pressure shall exceed the 



6l2 MECHANICAL ENGINEERING OF POWER PLANTS. 

resistance of the exterior force which holds it shut. A valve 
of this type is, however, not a safety-valve in the true sense, 
unless as it lifts it should have sufficient area to allow steam 
to escape through the opening which will be made as fast as 
the boiler can make steam with all other outlets closed. In 
other words, the pressure in the boiler should not be able to 
rise above that for which the valve is loaded, even if all other 
outlets are closed and the fire burning with its normal or even 
its maximum capacity for steam-making. Comparatively few 
safety-valves are of this capacity, for reasons of cost and con- 
venience, but the presence of such a loaded valve acts as an 
alarm to give warning of the passage of the known pressure- 
limit, so that means may be taken to stop the generation of 
steam and an accumulation of pressure. 

. Furthermore, as the pressure does accumulate under the 
valve when open and blowing, it has a tendency to lift the 
valve higher and enlarge the outlet in many of its forms. 
Most of the legislative requirements concerning boilers compel 
a safety-valve of an accepted construction. 

326. Forms of Safety-valve. — The safety-valve for boilers 
is likely to be in one of five forms. Historically the first, 
now practically not used in America, is the method of weigh- 
ing the valve down by a direct weight, resting on its back or 
suspended to it from below (Figs. 400 and 402). The difficulty 
of this form is that with large valves and high pressures the 
weight to be used becomes considerable and inconvenient. 
In English practice, where the direct weight is still preferred, 
the inconvenience is mitigated by using a number of smaller 
valves to secure the necessary area and subdivide the weights. 
The second form is to replace the weight with a spring 
whose intensity can be graduated. This avoids the bulk 
of the direct weight, but is open to the serious objection 
that as the valve lifts the resistance of the spring increases. 
The springs are also liable to corrosion, which makes them stiff. 
This form was used in many cases where jar from motion was 
to be experienced, but has practically been entirely superseded 
by the fifth form. 



BOILER ACCESSORIES AND APPLIANCES. 



613 



The third is a very frequent type, in which the spindle 
of the valve is held downwards by the action of a lever 
carrying the resisting weight with a long arm, while the 
effort of the valve to overcome the weight has but a short 
lever-arm. This does away with the inconvenience of a great 
weight, and makes adjustment of the pressure to hold the 
valve shut both easy and rapid. It is probably the most 
widely prevalent form of safety-valve for stationary boilers. 
The objection to it is the tendency of the lever in its rise to 
cause the valve to become jammed from the oblique motion 
around the fulcrum of the lever. It may also be urged as an 




Fig. 494. 

objection to it that the weight may be so easily increased 
by sliding out the regular weight or by hanging other weights 
upon the lever. It is also easy to stop the valve from operat- 
ing by wedging it so that it cannot open under any pressure 
whatever. The lever-valve construction lends itself to a de- 
sired use in river-boat practice. By attaching a rope or chain 
to the end of the lever and leading it up over a pulley, with 
a weight on the free end, that weight acts negatively and 
takes weight off the valve, and lightens the pressure at which 
the valve will open when the engine is at rest. By hanging 
this second weight up so as to leave the rope or chain slack 
by which it is attached to the lever, the entire counterweight 
comes on the lever, and full pressure is restored for regular 
running. 



'GTNEERING OF POWER PLANTS. 

For locomotive use before the fifth form was introduced it 
was usual to replace the weight by a spring which acted at the 
end of a lever to hold the valve down. This spring was 




Fig. 495. 



arranged so that the tension upon it could be varied by the 
engine-runner. It never became widely used outside of loco- 
motive practice. 

The fifth form is what is called the pop or reaction safety- 
valve, which is practically universal in locomotive practice, 
and is widely extended elsewhere. The principle of the pop- 



1 



BOILER ACCESSORIES AND APPLIANCES. 615 

valve is that, as the valve proper lifts from pressure, the escap- 
ing steam, instead of passing out directly from under the valve, 
must find its way out, after undergoing a change of its direc- 
tion in an annular groove formed in the valve outside of its 
inner bearing. The force due to the reaction of the steam in 
escaping adds an additional effort to lift the valve, increases 
the opening thereby, and with a given loading the valve will 
remain open until the pressure within the boiler has fallen 
perhaps 5 pounds below that at which the valve lifted. The 
additional area exposed to pressure when the valve lifts causes 
it to open with a sudden motion which has given it its ordi- 
nary name, and it also closes suddenly when the pressure has 
fallen. Figs. 494 and 495 show types of lever and pop safety- 
valve. 

A failure of the safety-valve is often due to corrosion 
either of the valve upon its seat or of the guiding-spindle in 
its guides. The safety-valve, therefore, should be frequently 
lifted by hand in order to be sure that corrosion has not made 
it worthless, and a further safeguard is secured by the use of 
metals in the valve or seat which do not rust tosfether. 
Nickel has been applied for valve-seats with success by reason 
of its being a non-rusting metal, and certain bronze alloys are 
used for the same reason. Data concerning the area of safety- 
valves will be found in the notes. 



CHAPTER XXVII. 

CARE AND MANAGEMENT OF BOILERS. 

327. The Firing. — The firing of a boiler-furnace is to be 
done in accordance with the general principles of combustion, 
and the application of these to fuels which differ so widely 
makes it difficult to give anything but the most general sug- 
gestions. References also have been made in other connec- 
tions which bear on this subject. The three usual methods 
of firing are the spreading method, the side-firing or alternate 
method, and the coking method. The spreading method is 
to keep covering the fresh and incandescent coal on the grate 
with thin layers of fresh coal thrown in at short intervals. 
This is the usual and most successful method with anthracite, 
where best results are secured when the fire is least disturbed. 
Side-firing is to divide the furnace into two halves lengthwise 
and charge the fresh fuel on one, while the other is in its best 
state of incandescence. This has been referred to under the 
double Cornish or Lancashire method as a means of keeping 
up the temperature of combustible gases, and is especially 
applicable to bituminous coal. The coking method is to 
divide the fire crosswise instead of lengthwise, and charge the 
fresh coal containing gas at this front part or on the dead- 
plate, and push it backwards when the gas has been distilled 
off by the radiant heat of the fire behind it. The thickness 
of the fire will be determined by the draft and the quality and 
size of the fuel. Anthracite fires will be as a rule thinner than 
bituminous, and small coal will require a thinner fire than the 
larger sizes. With anthracite firing from 4 to 8 inches is 
accepted good practice, and with bituminous coal from 10 to 
16 inches. 

616 



CARE AND MANAGEMENT OF BOILERS. 617 

The starting of fires in the boiler-furnace is also a matter 
which varies with the fuel and the conditions of draft. If the 
chimney is reluctant to draw from its being cold, it can be 
helped by starting a little wood-fire in the base of the stack 
and beyond the boiler-setting, so as to create the first action 
of the chimney before the resistance of the setting is inter- 
posed. ■ It must be remembered that anthracite ignites reluc- 
tantly and large quantities of wood are necessary to get it 
well started. 

328. Cleaning Fires. — The interval between cleaning of 
fires will depend on the rapidity of the combustion and the 
quality of the fuel with respect to ash.- With anthracite fires 
it is usually only necessary to clean fires in stationary practice 
about four times in twelve hours. With bituminous coal it 
must be done more frequently, and often the best results are 
obtained by pulling the fire about at short intervals, which is 
fatal to the satisfactory working of an anthracite fire. The 
cleaning is done by means of slice-bars which break up the 
clinker and separate the combustible from the incombustible 
matter, and after the fire is thoroughly broken up the aggre- 
gations of incombustible matter are removed by a rake or hoe. 
What remains is then spread evenly over the grates, and a 
fresh charge of fuel thrown on the fire. The ashes and clinker 
drawn out from the furnace will then be extinguished and 
cooled by a jet of water from a hose, and will then be 
removed. Care must be taken in handling the extinguishing 
water that it should not strike by accident any of the hot 
castings about the ash-pit, which it would be certain to crack. 

329. Banking Fires. — It is usually the least trouble and 
expense to bank the fire at the close of the da)^ or when the 
fire is to be kept over for some hours during an interval of 
inaction. After the fire has been cleaned, what remains in the 
grates, instead of being spread evenly, is piled against the 
bridge-wall and upon the back half of the grates, leaving the 
front part bare. Fresh coal is then charged in a thick layer 
over the banked fuel, and the fire is left with the ash-pit doors 
closed, the fire-door open, and the damper closed, or nearly so. 



6l8 MECHANICAL ENGINEERING OF POWER PLANTS. 

The closure of the ash-pit and the access of cold air above 
the fire make the ignition of the bank of fresh coal very slow, 
so that several hours will elapse before it has become ignited, 
and even then it burns slowly and not actively. At the end 
of the time, determined by the quantity of fresh coal used in 
banking, the fire is cleaned and spread, and is ready for a new- 
campaign. 

330. Regulation of the Fire and Pressure of Steam,— 
The regulation of the fire is done by controlling the access of 
air to it whereby combustion is stimulated or checked. The 
closure of the ash-pit and the damper check the fire, and to 
open them stimulates it. The fire-door opening into the 
furnace above the grates is a further means of controlling the 
fire in part, since by opening it cool air comes in to lov;er the 
temperature in the fire-box, and without passing up through 
the coal it does not stimulate combustion. The cool air further 
checks the making of steam by cooling the products of com- 
bustion, and acts by contact as a cooling medium passing over 
the heating-surface and through the tubes. It has already 
been noticed that this is not a desirable thing to do, by reason 
of its effect on the metal of the boiler, but it is an efficient 
method of control. 

The steam-pressure is controlled by the fire principally, 
but it can also be regulated by the use of the feed-water. 
The introduction of cool water cools the contents of the 
boiler, and checks partly or altogether the formation -of steam. 
The presence of additional water, furthermore, makes addi- 
tional material to absorb heat-units, so that great skill is to be 
shown when known variations for demands for steam are to be 
expected, by so controlling the times for feeding and the 
amounts fed that this storage of heat shall be utilized to its 
best extent. 

331. Cleaning the Heating-surface Outside. — The metal 
of the heating-surface in most boilers becomes coated with a 
scale of some non-conducting character caused by the light 
dust and ashes attaching themselves to the plate, and particu- 
larly when tarry matter is present in the products of combus- 



CARE AND MANAGEMENT OF BOILERS. 



619 



tion. Within the tubes of a tubular boiler a deposit of dust 
and ashes will also take place, perhaps choking the tubes or 




Fig. 496. 

at any rate rendering them less efficient. The cleansing of 
these exterior surfaces from the soft scale is done either 
with scrapers, or by brushes (Fig. 496), or by means of a 



620 MECHANICAL ENGINEERING OE POWER FLA A TS 



jet of high-pressure steam or air directed upon the surface to 
be cleansed from a nozzle (Fig. 497). The tube brush or scraper 
is passed through the tube and scrapes the surface clean, but 
the steam-jet acting at high velocity seems to have a special 
cleaning effect, and is used either independently or in connec- 
tion with the scrapers. Special forms of such steam-cleaners 
are used in which the jet receives an annular form and a spiral 
motion (Fig. 497), but very good results are obtained by 




Fig. 497. 



means of a simple short-length of pipe coupled to the steam- 
space in the boiler by means of a flexible hose. The settings 
of sectional boilers usually have openings made through their 
walls in which pipes are built, and through which pipes the 
cleansing jet of steam can be inserted at different levels, and so 
keep the surfaces up to their efficiency. The tarry deposit 
sometimes refuses to be moved by the steam-jet, when, of 
course, scrapers must be used. 

Locomotives are more often cleaned by air-jet, because of 
the danger to the person cleaning if any accident should occur 
to the hose joints while he is confined within the fire-box. 
With steam in use under these conditions, the cleaner would 
be burned before he could escape, while with compressed air 
there is no such danger. 

332. Boiler-scale or Incrustation. — It will be apparent 
that any solid matter in solution or present in, suspension in 



.. 



cai:e and management of boilers. 621 

the water fed to a boiler will remain behind in the boiler when 
the water is evaporated, because the steam will carry none of 
this material with it. If the salts in the water are of a soluble 
character, the process of evaporation will tend to concentrate 
the solution which remains in the boiler, and if they are in- 
soluble they will gradually fill up the water-space. Concen- 
tration of soluble solutions is prevented by the process of 
blowing down (par. 324), but for the removal of the insoluble 
matter some special procedures or appliances must be used. 

The soHd matter which gives trouble inside of boilers is 
introduced either in suspension or in solution. When it is in 
suspension the water is called a muddy water, and the proper 
procedure is to filter the feed-water for the removal of such 
suspended matter. This gets rid of the difficulty from this 
mud outside of the boiler altogether by preventing it from 
getting in. If this is inconvenient, the mud-drum will be a 
necessary feature of the boiler, and blowing off the accumula- 
tions must be practised at frequent intervals. 

A class of salts enters the boiler in solution, but is pre- 
cipitated as an insoluble precipitate on boiHng. These are 
among the most troublesome, because they are really formed 
within the boiler itself, and consequently can only be pre- 
vented from getting in by chemical reactions of some magni- 
tude. The salts of this class are the carbonates of the alkaline 
earths, lime and magnesia, and the sulphate of lime, which 
is the most troublesome of all. The feed-waters which are 
usually drawn from fresh-water sources are not likely to 
contain much sodium or potassium, which form the soluble 
salts, but in sea-water the chloride of sodium and magnesium, 
which are both soluble, are elements which give it its salty 
taste. Silica, alumina, and organic matter are to be found in 
some of the Western waters, or where the wash of surface- 
water may have come into the source. 

Great difference in the difficulty of the problem of dealing 
with boiler- scale results from the form which the scale takes. 
The carbonates of lime and magnesia are a mud — white or 
grayish in color when pure. They have no cementing ten- 



622 MECHANICAL ENGINEERING OF POWER PLANTS. 



dency and can be treated like suspended impurities. Silica 
and the sulphate of lime, however, are crystallizing bodies in 
the water which form into a hard adhesive crust, and not only 
this, but they Tiave the property of causing the carbonate 
scales to crystallize with them and add to the extent and thick- 
ness of the adhesive coating. The following table shows the 
properties of these most prevalent scales, and their degree of 
solubility at various temperatures. They enter the boiler as 
the bicarbonate, which is soluble, but on boiling one part of 
carbonic acid is expelled, and the protocarbonate which 
remains is the insoluble form. The carbonate of magnesia is 



Salt. 


Temp. 
Deg. Fahr. 


Authority. 


Parts by Weight of 

H2O to Dissolve i pt. 

of Salt. 


Grains to 
Gallon. 


CaCOa and MgCOa 


62 


Bucholz 


41,600 to 62,500 


1.4 to 0.9 


(< <( <( 


212 


" 


16,000 to 24,000 


4.25 to 2.75 


(( (< << 


285 to 300 


Couste 


Insol. 





(( <« a 


62 


B. 


461 


126 


CaS04 


95 


Regnault 


393 


178 


<< 


212 


R. &B. 


460 


126 


<< 


290 


R. 


Insol. 






a light flocculent powder which usually floats at or near 
the surface of the water, rather than sink to the bottom. 
Organic matter is apt to act in the same way, especially when 
it is of a vegetable character. 

333. Inconveniences Due to Boiler-scale. — The presence 
of the solid matter in the water of a boiler may do harm in 
one or more of four ways. 

(i) If it forms hard and solid over the heating-surface, it 
adds a non-conducting thickness to the evaporating-surfaces, 
so that an excess of fuel is burned to make the required 
quantity of steam. 

(2) This non-conducting covering causes the metal of the 
boiler to be overheated because the water does not cool it. 
This may produce an injury which is general or local. The 
general deterioration all over comes from an oxidation of the 
plate on the outside, because its high temperature makes the 



CARE AND MANAGEMENT OE BOILERS. 623 

oxygen reactions more rapid than they would be if the plate 
were cool. The local injury comes from the presence of a 
thickness of scale at points exposed to intense action of fire, 
whereby they become practically red-hot and softened, so as 
to yield under the internal pressure. Bags or blisters result 
from this trouble, which is aggravated if grease has become 
mixed with the scale at the point in question. A lump of 
scale is sometimes carried by circulation and dropped in a 
special place, and becoming attached there, a local overheat- 
ing begins underneath it. 

(3) The scale which crystallizes, accumulating in feed- 
pipes, blow-off pipes, water-gauge connections, and the like, is 
occasion for trouble in the use of these appliances (Fig. 483). 
In sectional boilers, besides the annoyance from the first 
two causes, the presence of scale impedes the rapid circula- 
tion, and increases the troubles which are met from this 
difificulty (Chapter XXI). 

(4) The presence of the floating mud or flocculent precipi- 
tate causes the boiler to prime, because the steam-bubbles 
must force their way through the scum at. the disengaging- 
surface, and in doing so water follows upwards with the 
steam, and is entrained mechanically through the steam-pipe. 

The ill effects or injuries caused by scale are to be miti- 
gated or avoided by methods which can be grouped under 
three heads. The first is the removing of the scale which is 
allowed to form. The second is the preventing of the solidifi- 
cation of the scale either by changing its character or by 
other means, and then causing its removal by methods of the 
first class. The third is the purification of the feed-water 
from its impurities before it enters the boiler. 

334. Removal of Boiler-scale. — When the scale is a mud 
and without tendency to cake upon the heating-surface: 

(i) The boiler can be allowed to cool down full of water, 
and when cooled emptied through the blow-off pipe. By 
removing the manhole and entering the boiler with hose-jet 
and brooms, the accumulations of soft scale can be washed 
out and the boiler is clean. 



624 MECHANICAL ENGINEERING OF POWER PLANTS, 

(2) The mud can be prevented from accumulating and 
with an efficient mud-drum can be removed, by blowing the 
boiler down at short intervals during the day, and blowing it 
out completely at the end of a week or oftener. The objec- 
tion to this method is that the scale which is not thoroughly 
washed out by the outflow through the blow-off pipe will dry 
on the heating-surfaces in cakes which it is difficult to remove 
when it has once solidified. 

When the scale is of the character which cakes on the 
metal of the boiler, due to the presence of sulphate of lime^ 
two methods can be used. 

(i) The boiler being emptied of water and cooled empty, 
a brisk fresh fire is started under the empty boiler. The 
effect of this is to expand the iron at a rate faster than the 
scale, and causes the latter to crack off in flakes, which are 
then swept out after the boiler is cooled again. The objection 
to this is a fatal one, in that it is very hard on the boiler and 
injures it. 

(2) A more usual plan is to allow the boiler to cool, empty 
it, and enter it through the manhole with what is called a 
scale-pick. This is a species of hammer with both faces 
formed to a wedge, and with it the scale is struck and broken 
very much as a film of ice is broken off the exposed stones of 
dwellings or pavements in Northern cities. The objection to 
this method is that the forcible removal of scale carries with 
it the film of oxide of iron which is formed on the inside of a 
boiler, and which adheres to the scale rather than to the iron. 
The ultimate effect is to thin the iron by this continual 
removal of the oxide film. 

Belonging to this same class of methods is the use of an 
apparatus in the form of a trough or false bottom inserted 
within the boiler, and so arranged as to catch the precipitate 
which is moving with the currents of circulation. When the 
solid matter has fallen into such pan or trough it no longer 
is exposed to circulation, but lies where it has fallen, and 
therefore does not have a chance to get to the real heating- 
surfaces. This, of course, is a method available in shell boilers 



CARE AND MANAGEMENT OF BOILERS. 625 

only. For the flocculent or floating type of scale a blow-off 
connection at the surface of the water in the boiler has been 
found convenient. This has been arranged to have a trumpet- 
shaped mouthpiece whose amplitude is greater than the 
normal range of the water-line in blowing down, so that when 
the attached valve is open, surface-water flows into the 
trumpet mouth and out of the boiler, carrying with it the 
floating scum. In sectional boilers the main dependence 
against the adhesion of scale within the small units which 
make it up is the rapid circulation (see Chapter XXI), but 
special cleansing tools have been devised to meet this problem, 
in which an appliance driven by steam or air can be intro- 
duced within the tube. It has cutting or impact tools which 
break up and loosen the scale so that it can fall out or be 
swept away. 

335. Prevention of Scale-formation. — There are three 
great methods which are used to prevent the scale from form- 
ing a hard adhesive crust or coating. The first of these is to 
introduce in a boiler some reagent or material which shall 
prevent the scale from hardening or crystallizing by a sort of 
mechanical reaction. This is the basis of methods which 
have been used involving the introduction of sand, saw- 
dust, malt-grains, and similar material which shall form 
the nuclei around which the scale is to solidify in the form 
of balls or larger grains, and remain in a form easily 
removable. 

The second method has been to make use of some material 
in the boiler which shall act as a varnish caked upon the sur- 
face of the boiler, so that the adhesion of scale should be 
made more uncertain. The introduction of kerosene, starch, 
or the real varnishing of the surface with some suitable com- 
position all operate in this way. Perhaps kerosene is one of 
the best known of the reagents of this class, and for many 
waters seems to be the best to be used in this way. It is 
introduced either gradually by a small connection to the feed- 
pipe suction, or a charge is put in at intervals. Mineral oil 
or grease does not meet the case, by reason of the tendency 



626 MECHANICAL ENGINEERING OF POWER PLANTS. 

v/hich it has to adhere itself to the heating-surface, and by 
keeping water from contact with the metal cause overheating 
as badly as the scale itself, if not worse. 

The third method is to introduce a reagent which shall act 
chemically on the precipitate either to change its crystallizing 
or solidifying character, or to change an insoluble into a solu- 
ble salt. The reagent may either be an acid or a salt. 
Among the acids, tannic and acetic acid are perhaps the most 
usual and preferred by reason of their reaction upon the sul- 
phate of lime, and the relatively mild action which they have 
upon iron if the acid should not find sufficient base in the feed- 
water and remain free. These acids are introduced in the 
form of brewer's grains, molasses, oak-bark, etc., or in the 
form of a liquid or crystalline acid. The difficulty with this 
method is the danger to the metal of the shell itself. In 
some few places where an acid water has been at hand it has 
been alternated or mixed with the basic water so as to oppose 
them to each other's action. 

The salts which are used are either the carbonate of soda, 
the chloride of barium, the tannate of soda, and the sodium 
triphosphate. The reactions of these with the sulphate of 
lime form a non-adhesive precipitate, and the soluble salt 
which results from the reaction with the lime is removed by 
blowing down. The proportions of salt to be used with any 
water are to be determined on the basis of chemical analysis. 
To this class belong also the methods of which the use of 
zinc suspended in the water is a type. While the scientific 
basis for the practice is not clear, its practical success in many 
cases for the purpose desired cannot be questioned. 

336. Previous Purification of Feed-water. — The method 
which stands on the highest scientific plane with a boiler pJant 
which must use a bad feed-water is to prevent the solid matter 
from getting inside the boiler at all. There are several 
methods for attaining this object. 

(i) The use of such forms of feed-water heaters as may 
properly be called lime-catchers. The feed-water is heated 



CARE AND MANAGEMENT OF BOILERS. 



627 



in the heater to a point at which it precipitates all or most of 
its soHd matter (pars. 321 and 322). 

(2) The use of the methods of surface condensation which 
prevail in marine practice, whereby the same distilled water is 




Fig. 498. 

used over and over again and no additional solid matter is in- 
troduced with the feed-water, except with so much of the 
latter as may have to go in to supply leakage and waste 



628 MECHANICAL ENGINEERING OF POWER PLANTS. 



(Figs. 70 and 71). The use of impure water to cool the sur- 
face condenser is entirely admissible. 

(3) A previous purification of the feed-water by che-mical 
means. This means that the feed-water to be used in any 
day is introduced into a tank, and into such tank is thrown the 
necessary reagent to throw down the solid matter in the water. 
The milk of lime or hydrate of lime will transform the soluble 
bicarbonate into the insoluble protocarbonate, and the chloride 
of barium will form the sulphate of barium with the sulphate 
of lime. The precipitate thus formed can either be filtered 
out, or it can be allowed to settle and only the clear liquid 
is pumped into the boiler which contains the soluble sulphate 
constituents which remain after the reactions. The disad- 
vantages of this method are obvious in the cost of the tank- 
age, and the room which it will occupy, and the cost of the 
reagents used in the process 




Fig. 499 



337. Filtration of Feed-water. — The filtration of feed- 
water either for the removal of suspended solids, or of pre- 



CARE AND MANAGEMENT OF BOILERS, 629 

cipitates, can be done in open filter-basins, or in close or 
pressure filters. The open filter-basin is the usual water- 
works method, whereby the water is made to pass through 
layers of gravel, sand, and charcoal in succession, and in each 
of which a certain proportion of the suspended material is 
caught and only the clear liquid passes through. The pres- 
sure filters operate on the same principle of forcing the feed- 
water through layers of successive fineness, but this will be 
done in a closed tank and under pressure instead of depending 
on the simple head due to gravity. Most of these filters 
operating under pressure are arranged to be reversible either 
by three valves, or a system of equivalent pipe-connections, 
so that the accumulated mud in the layers of the filter can be 
washed out by such reversed current. Otherwise provision 
must be made at intervals to remove the filtering material, 
cleanse it, and replace it, during which the water either goes 
unfiltered or is filtered through a duplicate or reserve appa- 
ratus (Figs. 498, 499). Consult also par. 197 on oil-filtration. 

338. Deterioration or Wear and Tear of Boilers. — The 
conditions to which a boiler is exposed in service tend to wear 
it out. Many engineers have felt so strongly on this point 
that they have proposed to limit the life of a boiler in use, 
and to specify that a boiler is good for ten years, may be run 
at reduced pressure after fifteen years, but should be thrown 
out at the end of twenty. The causes which tend to wear out 
a boiler are partly inherent and unavoidable, and partly acci- 
dental so as to be avoided by care. The avoidable ones are 
usually acute forms of the sources of deterioration which are 
inherent and unavoidable. Deterioration of boilers is caused 
by overheating, by unequal expansion and contraction, and 
by corrosion. 

339. Overheating of Boilers. — An injury to the heating- 
surface of a boiler from overheating is usually due to careless- 
ness either in permitting the water-level to get so low as to 
expose the heating-surface uncooled, or to the presence of 
scale or grease. These have been already referred to in the 
previous paragraphs. The furnaces of internally-fired boilers 



630 MECHANICAL ENGINEERING OF POWER PLANTS. 

and the tubes of sectional boilers are particularly liable ta . 
injury from overheating caused by grease. In sectional boilers, 
besides the oxidation due to overheating, a strain of great 
magnitude is set up in the straight-tube boilers, where the 
tubes tend to become of unequal length. In some forms of 
sectional boilers also, in which disengagement is inadequate 
and circulation impeded, a section may become overheated 
because the water cannot reach the metal. Sectional boilers 
whose units cannot be cleaned are especially open to the 
danger of overheating. 

340. Unequal Expansion and Contraction of Boilers. — 
The- intense action of the fire upon boilers tends to raise the 
temperature of the metal forming them, while an impact of 
cold air or cold water produces a tendency to cool and contract 
that metal. Where this action is local the boiler has a 
tendency to stretch out of shape, and strains are brought 
upon its structure which act to wrench and destroy the boiler, 
causing leakage and deterioration. These changes of shape 
may produce several consequences. 

(i) In fire-tube boilers they cause a leakage of the joints 
v/here the tubes are expanded into the heads. 

(2) The boiler has a tendency to change its shape, and 
therefore to alter the distribution or the proportion of strain 
which comes on its various lugs or supports (par. 266). In 
shell boilers this change of shape may produce such a super- 
position of strains as to cause a boiler to give way under them 
at a point where such combined strains may be concentrated. 

(3) If there are any defective welds in the plate of which 
the boiler is made, contraction of the layers of skin causes 
that lamination to extend, and finally to develop a blister or 
bag. In steel plate a blow-hole will be the occasion for 
similar action. 

(4) The contraction and expansion of a boiler with 
lapped joints produces an effect which has been called 
"grooving." The effort of the two contiguous plates to 
flex into line with each other when they are pulled length- 
wise (pars. 214 to 218) causes the protecting scale of oxide 



CARE AND MANAGEMENT OF BOILERS. 



631 



of iron to be broken off at the point of greatest flexure. 
Fresh rust forming there and again broken off by the flexure 
of the joint results ultimately in the 
erosion of the metal, and the for- 
mation of a groove at this point, 
whereby the strength of the plate 
is gradually reduced. Figs. 500 and 
501 show a groove of this sort and 
its location. They are often deep 
enough to take the blade of a knife, 
and are to be detected in most cases 
by its use. They are also revealed 
frequently by the presence of a stain 
of oxide of iron upon the scale re- 
moved from the plate around the 
joint. Grooving is made worse when 
there are acids in the water, and 
where the flexible part of the shell 
is joined to a stifBy-stayed or inflexi- 
ble part, so that the bending action 

is concentrated. Such a place is the 

joint of the flange of the head of a 

boiler with the flat surface of the 

head. 

341. Corrosion External. — The 

third source of deterioration of boilers 

is the corrosion to which they are 

exposed from the conditions of their 

use. This corrosion takes place from 

the inside of a boiler and from the 

outside. 

External corrosion may be the 

result of any or all of the following 

conditions: 

(i) The action of the hot gases upon the heated plate 

which forms the heating-surface. If the fire is forced, or if 

the surface is covered with a thin scale which prevents rapid 




Fig. 500. 




Fig. 501. 



632 MECHANICAL ENGINEERING OF POWER PLANTS. 

transfer of heat, the metal will be heated so that it will react 
with oxygen in the gases and become rusted or corroded. 
This difficulty is aggravated by the presence of moisture in 
the gases, either from the coal, as water present mechanically, 
or from the combustion of hydrogen to water. This condition 
is favorable to rapid action on the iron from carbonic acid, or 
sulphurous acid resulting from the oxidation of carbon, or sul- 
phur in the fire-box. 

(2) From leakage. This may occur from seams, around 
rivets, where the tubes enter the tube-sheets, around the dome- 
joints, and at the joints of the hand-holes or manholes in shell 
boilers. In sectional boilers, in addition, will be the leakage 
caused around joints of the caps and that which is caused by 
unequal expansion of tubes in their headers. In internally- 
fired boilers, where the water-legs are closed by massive rings 
at doors and bottoms, leakage is apt to occur from differences 
of temperature due to defective circulation. The leakage 
from valves which are not thoroughly packed or tight upon 
their seats is also a further occasion for corrosion. This 
moisture not only corrodes of itself, but is the occasion for 
forming an active corrosive agent with carbonic acid; and if 
the water exerts any mechanical action upon the rust, scales 
tend to loosen and expose fresh surfaces to corrosive action. 

(3) The presence of lime in the setting of brick-set boilers 
is another occasion of external corrosion. The heat of the 
fire and its gases causes the lime to become calcined to the 
hydrate, and in this form it is likely to exert a corrosive in- 
fluence where it touches the metal. 

External corrosion is to be detected by -careful inspection, 
and the setting of the boiler should be such that this inspec- 
tion should be possible. 

342. Corrosion Internal. — The corrosion which takes 
place inside a boiler is more rapid and injurious than the 
external corrosion. It may be due to one or all of several 
causes. 

(i) The presence of acid in the water undergoing evapora- 
tion. The source of this acid in the water is often determined 



CARE AND MANAGEMENT OF BOILERS. 633 

by local conditions. In the mining districts where sulphur 
prevails in the coal or in the surface-water and, worse than 
that, in the mine-water, the sulphurous acid which results is 
very actively corrosive upon iron. Nitric acid in the form of 
decomposable nitrates and nitrites is present in waters which 
have been contaminated with sewage or which contain organic 
matter. Water from bogs or peaty deposits containing 
vegetable matter in decomposition will contain the earthy or 
humous acids, formic, etc. 

(2) Perhaps most trouble in boilers is caused by the corro- 
sive action of the acids due to decomposition of the lubricants. 
The reaction on boiling animal oils, tallow, etc., breaks such 
material up into stearic and oleic acids, both of which are 
corrosive to iron. The oil comes into the boiler with the 
feed-water from condensing engines where pains are not taken 
to prevent it (par. 197), and will undergo this trying-out 
process. The active element of corrosion in sea-water and 
water used in marine boilers is hydrochloric acid, which re- 
sults when the chloride of magnesia present in sea-water is 
boiled. The heat decomposes the chloride into the hydrate 
of magnesia and hydrochloric acid, which latter attacks the 
iron. 

(3) From galvanic action between the iron of the boiler 
and some metal which is electropositive to iron. Such metals 
are copper and brass, which form with iron a galvanic couple, 
and in waters containing even weak acids, like carbonic acid, 
the iron undergoes oxidation and corrosion. Such metals for 
galvanic action would be found in copper stay-bolts, tubes, 
ferules, and even in brass mountings of fixtures for feed-con- 
nections. Sea-going boilers are particularly liable to this kind 
of corrosion by reason of the presence of the acids in sea- 
water, and it has been found a convenient thing to hang a 
piece of zinc in the water-space of such boilers in order that 
by its presence, which furnishes a lower electric potential, the 
zinc might be the element attacked rather than the boiler 
itself. 

(4) Distilled water containing carbonic acid seems itself 



634 MECHANICAL ENGINEERING OE POWER PLANTS. 

to be corrosive of iron, under the conditions which prevail 
within a boiler. Laboratory experiments have not always 
been conclusive on this point, except with respect to water 
containing no air but carrying carbonic acid. 

(5) The water seems to have an erosive action mechani- 
cally against surfaces upon which it is thrown violently by the 
currents of steam in which the water will be carried in drops. 

Spattering followed by drying of the spattered water 
seems also to wash off and loosen the scale of oxide of iron 
and produce the effect of corrosion. 

The corrosion due to water is to be expected below the 
water-line or where the mechanical action of water may make 
itself felt near the water-line in the steam-space or in the pipe- 
connections. 

. Corrosion, however, is often met in the steam-space of the 
boiler and manifests itself with somewhat of capaciousness. 
It has been found that a boiler in the steam-space may be kept 
quite hot by the non-conducting covering over it, and some- 
times causes the corrosion to manifest itself more rapidly by 
reason of the high temperature producing a considerable ex- 
pansion, and at a rate different from that of the oxide of iron,, 
so that the oxide is cracked off and fresh surfaces exposed. 

343. Pitting, Wasting, and Grooving. — The corrosion of 
a boiler on its internal surfaces usually takes place in one of 
three forms. The wasting is a gradual thinning of the plate 
all over, due to a uniform acid action whereby the iron is 
dissolved. It is not always easy to detect this, except by 
close inspection of the joints, and the indications around the 
rivets which show what the original and unreduced thickness 
of the plate should have been. 

Pitting is a curious and capricious eating of the plate in 
spots. The reasons for local corrosion of this sort are not easy 
to find. It is doubtless often due to lack of homogeneity in 
the plate, so that it has been more exposed to yield to corro- 
sive influence where cinders or similar impurities are present. 
Mechanical errosion is apt to produce the effect of pitting. 

Grooving is the corrosion which has already been referred 



CARE AND MANAGEMENT OF BOILERS. 635 

to in paragraph 340 where the changes of shape cause a 
mechanical breaking away of the oxide of iron formed, so that 
fresh surfaces are continually exposed. When corrosive ten- 
dencies are present in the water, grooving goes on so much 
the more rapidly. 

It is a matter of discussion as to the best preventive of 
corrosion in boilers which are to go out of use. Some advo- 
cate the plan of preventing access of air by filling the boiler 
full of water. Others dry out the boiler by putting a char- 
coal fire in a brazier within it which disposes of the oxygen 
also, and any remaining moisture is absorbed by hydrate or 
chloride of lime. Then the boiler is closed. This is the 
English naval practice. 

Minute and painstaking inspection of the interior surfaces 
of a boiler is necessary if danger from corrosion is to be 
guarded against. 

344. Repairs. General. — The repairs to a boiler are of 
the same nature as the operations in its construction so far as 
leaky seams or tubes and joints are concerned. The leakage 
at a tube-joint can be prevented by expanding once or twice, 
but after that the metal becomes hard or brittle and further 
expanding cannot be done. Locomotive-tubes are particularly 
liable to trouble of this sort, and the custom has prevailed of 
cutting the tube off at its two ends and inserting a short 
length at one end which should bring fresh and unfatigued 
metal to make the joints at the tube-sheets without renewing 
the entire tube-body. The piecing out of the tube is done 
by making the two ends to l?e joined into a male and female 
cone, and then welding the lap of the two surfaces over a 
mandrel. In sectional boilers the repairs are usually re- 
newals of the tubes in detail, the regrinding of joints be- 
tween the caps and headers, and the like. All boilers with 
manholes will require that the gasket shall be renewed periodi- 
cally, and usually at each time that the manhole-lid is re- 
moved for purposes of cleansing and inspection. On shell 
boilers, however, it may be necessary to apply a patch. 

345. Patches. — The failure of a part of the metal in a shell 



636 MECHANICAL ENGINEERING OF POWER PLANTS. 

boiler where the entire plate does not have to be renewed may 
be repaired by putting a patch on the defective part. Such 
patches are of two kinds, the hard patch and the soft patch. 
The patch will be put on a boiler by cutting away the metal 
which has deteriorated, leaving a hole where the defective 
metal has been and including enough to come to the solid and 
unaffected metal around the edge. A piece of boiler-plate is 
then shaped to the surface which it is to cover, and of a size 
to cover the hole and lap over its edge so as to be riveted to 
the shell in lap-joint. The necessary holes are then drilled 
and the patch is riveted on in place and calked. Such a 
patch is as good as can be made, but a patched boiler is never 
as good as the unpatched plate, and the presence of patches 
usually indicates either defective material or hard usage. 

The hard patch just described will be used wherever possi- 
ble, but it can only be used where riveting can be done. If 
the patch must be made at a place where riveting is impossi- 
ble, the patch will be secured in place with bolts, but they 
will not make the joint as tight as the rivets, and consequently 
a packing of some sort must be inserted between the two 
plates and also around the bolts. This packing is usually for 
the ordinary soft patch a cement of red lead mixed to a paste 
with oil, and held by being formed into a rope or gasket by 
working it into unwoven lamp-wick. A rope of this paste and 
wicking is laid around on the inside of the bolts in the lap of 
the patch, and is compressed to fill the joint and make it tight. 
Such a patch, however, is not as reliable as the hard patch, 
and is liable to blow out under heat and deterioration com- 
bined with pressure. 



CHAPTER XXVIII. 

BOILER INSPECTION AND TESTING. BOILER-EXPOSIONS. 

346. Boiler-inspection. — The steam-boiler being an en- 
gineering construction and exposed to known strains, it 
becomes necessary that the person responsible for it should be 
able to inform himself concerning its condition and ability to 
withstand these strains. This is to be done by means of 
inspection by the eye of experience and skill. It involves a 
knowledge both of accepted practice and of the causes which 
tend to wear out a boiler, and judgment in deciding how far 
they have acted either to render the boiler unsafe at its former 
pressure or unsafe to use under any conditions. A proper and 
full inspection, therefore, covers all the points which have 
been made the subject of discussion in Chapters XIX to 
XXVII hitherto, particularly with respect to corrosion in 
its various forms, the effects of overheating, and proper care 
and design with respect to bracing and staying, and also the 
use of satisfactory appliances for the management of the boiler 
and the relief of any excess of pressure. Further than this, 
the inspector should satisfy himself that the boiler is able to 
withstand its working pressure by exposing it to a pressure 
somewhat higher than that which it is expected to carry, and 
then observing whether under such pressure the boiler shows 
any signs of weakness, deformation, leakage, or similar failure. 
It is usual to expose the boiler to a pressure-test equal to one 
and one half times its ordinary working pressure. This is en- 
tirely safe with normal conditions, since tlie boiler was probably 
designed with a working pressure of one sixth of its calculated 
bursting pressure (par. 207), so that if exposed to three halves 

637 



638 MECHANICAL ENGINEERING OF POWER PLANTS. 

of one sixth of its bursting pressure, it is only tested to one 
quarter of the ultimate pressure. There are three ways of 
making this pressure-test. 

347. The Steam Pressure-test.— The steam pressure-test 
is to close the orifices of the boiler, increase the safety-valve 
weight, and building a fire under the boiler to make it test 
itself to one and one half times its working pressure. The 
advantage of this method is that it exposes the boiler to the 
conditions of service with respect to strains caused by heat as 
well as by pressure. The objection to it is evident; that if 
the boiler is to fail under its test, its failure, by reason of the 
presence of a volume of hot water, will be the occasion of a 
disaster. It should only be practised, if ever, where proper 
public safeguards can be applied. 

348. The Hot-v/ater Pressure-test. — The second method 
is to fill the boiler completely full of water, and with all out- 
lets closed start a fire in its furnace. The water will expand 
more rapidly than the iron forming the shell, so that the 
expansion of the water will bring a strain upon the shell from 
within which can be graduated to the required amount. 
When the pressure is reached the fire is withdrawn. Water 
expands ^^ of its volume in passing from 60° to 212° Fahr., 
and the boiler being full is subjected to this expanding strain. 
This method has somewhat the advantage of having the boiler 
warm or hot, but in case of failure or rupture of the shell the 
water escapes without doing great harm, since but little energy 
is stored in it. The heat condition, however, is not favorable 
to the inspection of the shell for deformation and leakage, and 
consequently the third method is more usual. 

349. The Cold-water or Hydrostatic Test. — The hy- 
drostatic test as usually made is to fill the boiler completely 
full of water, and then by means of a pressure-pump, operated 
either by hand or by power, to raise the pressure of the water 
in the boiler to one and one half times the working pressure. 
This is done in the cold; and while the boiler is subjected to 
this internal pressure it should be carefully examined for 
bulging of the heads or other deformations, and for leakage 



BOILER INSPECTION AND TESTING. EXPLOSIONS. 639 

which can be attributed to this tendency to go out of shape 
under pressure. Leakage will be manifest by the rapid 
lowering of pressure, since the comparative incompressibility 
of water makes a slight leakage release pressure very rapidly. 
By putting a test-gauge upon the connections of the pressure- 
pump the boiler-gauge can be tested for accuracy at the same 
operation (par. 304). The only objection which has been 
urged against the cold-water test is that it is a severe one, and 
may injure the boiler by overstrain, and that the pressure 
due to the water brought by the action of a pump is a dif- 
ferent and more exacting one than would be brought by 
the pressure of the steam. The rejoinder to this is that if a 
weakness is to be developed, it is immensely to be preferred 
that it should be developed while the test is on than in 
service, and the large mass of water in most boilers pre- 
cludes any very great concentration of the pump-pressure. 
The steam-pressure is a fluid pressure, and the water is as 
flexible and mobile hot as cold. The laws of most cities 
compel a hydrostatic test to be made once a year at least of 
all boilers which are under municipal control. 

350. The Hammer Test. — In addition to the hydrostatic 
test for the resistance of the boiler to pressure and the 
detailed examination within and without by, the eye of an 
inspector, much information as to the quality of the boiler as 
a construction will be given by means of a careful and ex- 
haustive examination with a light hammer. The blow upon 
a loose rivdt or a stay which is not doing its work will reveal by 
the difference in the resonance the difference in its condition, 
its looseness, or its over-strain. The hammer will also indi- 
cate and reveal defects in the metal of the shell, the presence 
of cracks and similar weakness which may lead to a failure. 
Where the plate has begun to laminate and the beginnings of 
a blister have occurred, the hammer-blow will show that the 
spot is no longer solid at the point struck. 

351. Boiler-explosions. General. — The disaster which 
is most feared in connection with a steam-boiler as a reservoir 
of accumulated energy is that which is called an explosion. 



640 MECHANICAL ENGINEERING OF POWER PLANTS. 

An explosion results from a very limited number of immedi- 
ate causes, but a large number of secondary causes may be 
looked for as bringing about the primary cause. 

The primary cause is a failure or rupture of the envelop- 
ing shell of the boiler due to a pressure or strain greater than 
the metal could resist. This interruption of the equiHbrium 
or the destruction of the reserve of metal strength may come 
about by two different ways. 

(i) The boiler may be too weak for the pressure, so that 
it ruptures at its working pressure. 

(2) The pressure may become too strong fof the boiler to 
withstand, and it ruptures at some point above working 
pressure. 

352. Boiler Ruptures because too Weak. — The boiler 
may fail because it cannot withhold the pressure within it by 
reason of one of four conditions: 

(i) The original pressure at which the boiler has ordinarily 
been worked may have been fixed too high for a structure of 
that material, design, thickness, and construction. Such a 
boiler never was safe from the very first day it was used. 

(2) The boiler, originally strong and able to withstand the 
working pressure, may have become weakened by age, wear 
and tear, corrosion, or abuse. 

(3) The boiler, exposed to normal working strain, may have 
superposed upon such strain an extra strain of contraction, 
local and sudden. This may come by low water and sudden 
introduction of fresh cold water on overheated plates, or cold 
air acting similarly. This is the rupture of which low water 
is apt to be the occasion. 

(4) A defect of workmanship or material which escaped 
inspection when the boiler was new may develop in service, 
and particularly under abuse. The boiler may not be as 
strong as it was supposed to be, and fails. 

It is obvious that the more familiar the inspector is with 
the construction and sources of deterioration of boilers, the 
more reliable is his judgment with respect to fixing the work- 
ing pressure upon an old boiler. It will be seen presently 



BOILER INSPECTION AND TESTING, EXPLOSIONS. 64 1 

that if the rupture of the shell is caused by working pressure, 
the disaster called an explosion will or will not follow accord- 
ing to the combination of conditions under which that rup- 
ture takes place. 

353. Boiler Ruptures from Excess of Pressure. — The 
boiler being strong, perhaps new, may have the pressure 
within it raised to such a point that it is unable to withstand 
it, and fails at its weakest point. This is the condition of 
explosions above the working pressure or at pressures ap- 
proaching the bursting pressure. This group of conditions 
has been the favorite field for erroneous theories with respect 
to the disaster called a boiler-explosion. Most of them have 
been based on the idea that an explosion of some sort takes 
place within the shell, creating a pressure suddenly within that 
envelope, which it could no more withstand than if a powder- 
explosion were to bring suddenly an enormous pressure upon 
such a flexible envelope. Those who have upheld this idea 
have explained the explosion from the union of oxygen and 
hydrogen, which are the gases of the water, supposing them 
to have been dissociated by an overheated plate occurring 
with the condition of low water. A second theory of this sort 
has been that by reason of low water and overheated plate a 
sudden rise of pressure results from the coming in of the feed- 
water, causing an explosive sort of pressure within the shell 
which it could not withstand. A third and similar theory is 
that the water in the boiler gets into the condition called the 
spheroidal state, in which the bubbles of water are kept away 
from the red-hot plate by a film of steam, and which bub- 
bles form steam with a concussive rapidity when that film of 
steam is forced out. This condition is met in forging or 
rolling where water is used on red-hot metal and then struck 
with a hammer. 

It is difficult to realize the above conditions in a boiler, 
and when an explanation without recourse to them is to be 
found from accepted principles it does not seem necessary to 
search for less obvious causes. 

Furthermore, it can be proved (see Appendix) that in a 



642 MECHANICAL ENGINEERING OF POWER PLANTS. 

boiler containing a relatively small weight of water, and par- 
ticularly with ample heating-surface, the time required to 
pass from a low pressure to a higher one, which may be 
called the dangerous pressure, becomes surprisingly short, 
so that in the absence of an efficient safety-valve, or where it 
is inoperative, the steam pressure to rupture the boiler may be 
reached very soon after the outlets from it have been closed, 
unless proper precautions be taken with respect to checking 
the fire. 

354. Theory of Boiler-explosions. — When it is remem- 
bered that the specific heat of water is unity, so that a large 
quantity of heat is absorbed in raising its temperature one 
degree, it will be apparent that when a large mass of water 
under high pressure lies within a boiler an immense reservoir 
of. available energy is at hand. 

The boiling-point of water increases with the pressure, so 
that if the pressure on the surface of the water in a boiler is 
suddenly released and drops to atmospheric pressure, or 
nearly to it, a large quantity of water will form steam-gas 
upon the release of such pressure without the addition of 
heat. When, therefore, a boiler ruptures under pressure and 
full of water, permitting the escape of steam instantly or with 
great rapidity, the tendency of the stored heat in the water 
is to cause it to form steam under the reduced pressure with 
great rapidity. The formation of steam-gas from water is 
easily comparable under these conditions to the formation of 
carbon, sulphur, and nitrogen gases in the combustion of gun- 
powder. Hence the rupture of the shell causing a release of 
pressure on the water brings about a condition analogous to 
the touching of a flame to a gasifying substance like powder, 
and the water flashing into steam-gas is the thing which ex- 
plodes. If this operation is retarded, the energy is gradually 
released in forcing the water out through a small hole, and 
-no disaster follows the rupture. This is the element of safety 
of the so-called sectional boilers. 

355. Energy Resident in Hot Water under Pressure. — 
It can be shown by a simple diagram that an enormous quan- 



BOILER INSPECTION AND TESTING. EXPLOSIONS. 643 



tity of energy is stored in a cubic foot of water at high pressure. 
If the base of the cyHnder in Fig. 502 be supposed to have 
one square foot of area, and at its bottom a cubic foot of 
water is enclosed below the piston, so that upon the applica- 
tion of heat to that water the piston would have a tendency 
to rise under one atmosphere of pressure on it, the water 
would form steam to fill 1700 cubic feet. If, however, the 
pressure be increased upon the piston, the speci- 
fic volume of steam at such higher pressure di- 
minishes while the amount of heat necessary to 
make the water into steam increases. The cubic 
foot of water at seven atmospheres or 103 pounds, 
instead of occupying 1700 cubic feet, would 
occupy but 274, because the piston would be 
held down by a pressure of 14,832 pounds. If 
it be conceived that similar water in the bottom 
of that cylinder was not quite hot enough to 
make steam at that pressure, but was hot enough 
to make steam at a somewhat lower one, it will 
be apparent that the water when the pressure was 
released would be able to lift such weighted 
piston through a good many feet. A simple 
calculation shows that if this energy be repre- 
sented in foot-pounds, it is able to carry the 
weight represented by a boiler-shell, or a part of 
it, through a good many hundred feet, and to 
produce the effects which have been observed to attach to 
the most disastrous explosion. 

356. Reaction in Boiler-explosions. — It happens not in- 
frequently that when the rupture of the shell from excess of 
pressure or weakness has permitted a partial escape of pressure, 
the water in the shell seems to be lifted by the sudden release 
of pressure on that side of the boiler, and the unbalanced 
pressure produces a reaction; or the water itself falls back 
against the part opposite the rupture, producing a strain which 
the already weakened shell cannot withstand, and thereby 
makes so large an opening for the release of pressure that the 



w 

El 




Fig. 502. 



644 MECHANICAL ENGINEERING OF POWER PLANTS. 

•formation of steam-gas is almost instantaneous, and the boiler 
is driven out of its setting as a rocket is driven by the reaction 
of gas behind it. As a rule the light portions of a boiler after 
rupture are found in the direction of the initial rent, while the 
more massive pieces are driven by the reaction of unbalanced- 
pressure in the opposite direction. This reaction-phenomenon 
resembles concussive ebullition in that a strain almost like a 
solid blow is brought by it against that part of the boiler 
which remains in place. 

357. Procedure when a Boiler is in Danger of Rupture. 
— It would be manifestly unwise to release the pressure sud- 
denly from a boiler which was already under a great strain 
and in danger of rupture. To do so would be to invite the 
reaction caused by the lifting of the water, and the possible 
superposition of strains from this cause. The opening of a 
large throttle-valve or of the safety-valve may act in the same 
way, and it is doubtless this combination of strains which, 
explains the frequent failure of boilers when the day's work 
is just beginning, and steam is turned from a boiler into a 
cold pipe, where it condenses and makes a reduced pressure, 
so that the steam rushes from the boiler at higher velocity 
than usual. A large valve should be opened with exceeding 
caution, slowness, and care under these conditions. 

The proper procedure is to withdraw the fire and permit 
the boiler to cool off gradually, and so permit the dissipation 
of pressure by these means. The fire can be checked by 
dumping it or by throwing ashes or dirt upon it. If great 
confidence is felt in the ability and strength of the boiler, the 
blow-off valve can be cautiously opened for the relief of pres- 
sure slowly through that opening. The heat stored in the 
water is thus disposed of, and after the boiler is empty of 
water it is comparatively safe. The escape of pressure 
through the blow-off valve is also unlikely to cause difificulties 
from reaction. 



CHAPTER XXIX. 
MANAGEMENT AND RUNNING OF ENGINES. 

358. General. — So many and so widely different are the 
types of engine and the work which they are to do that any- 
thing Hke detailed instructions is impossible. The best that 
can be done is to lay down certain general principles applica- 
ble either widely or universally, and leave the application of 
them in detail to the judgment and skill of the operator in 
each case. 

The most general case would be of an engine for a power 
liouse or similar plant, and the first distinction which will 
make a difference in procedure must be based on whether the 
engine is non-condensing or condensing. 

359. To Start a Non-condensing Engine. — The engine 
having been properly erected and all connections supplied 
(Chapter XVIII), the fly-wheel should be turned in such a 
position that the valves uncover the ports, and that there is a 
turning leverage for the pressure of steam to turn the crank. 
This is usually secured by having the crank in the first quad- 
rant of its revolution. If the valve-gear is detachable so as 
to be operated by hand, this is of less consequence; but if the 
engine has a positively connected valve-gear, and particularly 
a cut-off mechanism, it may happen that the steam-valve has 
come back to close the admission of steam, while there is 
still a turning leverage so far as the mechanism is concerned. 
Most large engines have notches in their massive fly-wheel 
whereby they can be turned by an ordinary bar, or any 
mechanical purchase may be brought to bear to put the crank 
in the required position. The drip-connections for getting 
rid of condensed water being opened, steam is carefully 

645 



646 MECHANICAL ENGINEERING OF POWER PLANTS, 

admitted through the throttle-valve by a very slight opening^ 
whereby it will be allowed to blow through and heat the pis- 
ton and the walls of the cylinder to a temperature sufficient 
to prevent excessive condensation. This also rids the steam- 
pipe of the water which has accumulated within it. In posi- 
tively connected valve-gears this will heat but one end of the 
cylinder, but where the valves can be operated by hand the 
steam can be admitted for warming to^both ends, and the 
whole mass of metal brought up to the necessary temperature. 
It is desirable, however, to leave the drip-connections from 
the cylinder open until after the engine has started. The 
cylinder being fully warmed up, which will be recognized by 
touch and by the high temperature of the drip-pipes, a little 
more steam can be admitted either through the wider opening 
of the throttle-valve, or through the more ample movement 
of the distributing-valves, so that sufficient pressure comes on 
the piston to start the engine. It becomes a matter of im- 
portance to store sufficient energy in the fly-wheel to carry it 
past its first dead-centre, on which otherwise it v/ould be 
likely to catch, and particularly if there is water in the cylinder 
whereby its motion can be arrested just at the time of getting 
ready to pass the centre. If this difficulty is not met, the 
engine will then take up its regular motion, slowly at first, until 
all danger from water shall be passed, and then gradually more 
steam is admitted until its regular rate is reached, at which its 
governor will take hold and control the supply of steam. 
The danger from the water of condensation is usually passed 
at the end of two or three complete strokes, but it may last 
longer, and it may occur from priming even under regular 
service. The drip-valves are therefore closed cautiously, to 
be sure that all water has been blown out. It will make its 
presence manifest by a characteristic snapping or cracking like 
the blows of a metallic substance within the cylinder, which 
once heard will always be recognized. The danger from 
water has already been alluded to. If the engine is one 
requiring its cut-off to be regulated by hand, and not by the 
governor as in link-motion engines, adjustable cut-off engines, 



MANAGEMENT AND RUNNING OF ENGINES. 64/ 

etc., the throttle-valve will usually be opened wide and the 
regulation effected by the use of such adjusting mechanism 
when the normal speed of the engine is attained. 

360. To Start a Condensing Engine. — Here again the 
variety of methods used to effect condensation makes it 
dif^cult to include all conditions (Chapter IV). If the engine 
is surface condensing, the circulating water will be started in 
motion before the main engine is started. If it is a jet-con- 
densing engine driven by independent air-pump connections, 
the vacuum in the condenser will be created before the main- 
engine is started by starting the independent air-pump. With 
the attached system or the gravity or siphon systems the 
vacuum must be created after the first steam is delivered to 
the condenser. With the attached system and large air-pump 
it is desirable to start the engine with the crank in such posi- 
tion that the first motion of the piston shall cause the working 
stroke of the pump to take place and create a partial vacuum 
in the condenser. Sometimes the vacuum is created in 
advance of starting the attached mechanism by permitting the 
condenser to fill with water, and attaching an independent 
pump to the condenser which shall draw out the water until 
its capacity for equalizing pressures in its ,own cylinder and 
the condenser are reached. In many cases the cool metal of 
the condenser will serve to effect the first condensation and 
create a sufficient initial vacuum for the engine to get its air- 
pump to work without difficulty. The drip-connections of a 
condensing engine are different from those of a non-condensing 
engine, because as soon as the engine has started the flow 
would be into the cylinder through them. For this reason 
they are either left off or are connected into the condenser 
piping. After the engine has turned its centres the handling 
of its condensing appliance will involve the control of the 
injection-water in jet or direct-contact condensers, and the 
speed of the circulating-pumps in the surface type. Since it 
may happen, in condensing arrangements where the air-pump 
and circulating-pump are driven from the same rod, that the 
full capacity of the circulating-pump is not required, while the 



648 MECHANICAL ENGINEERING OF POWER PLANTS. 

air-pump must work full stroke, a by-pass valve is usually 
made on the circulating connections, so that it shall be able 
to pass its own water round and round in part, and not be 
compelled to handle an unnecessary weight to effect conden- 
sation. The injection of jet condensers enters them by atmos- 
pheric pressure, so that the valve which controls need not 
usually be wide open. The operation of the condenser is 
regulated by the reading of the vacuum-gauge, which is grad- 
uated either from zero to 15 pounds of vacuum, or from zero 
to 30 inches of mercury. The vacuum is satisfactory if it 
reads over 13 pounds or 27 inches. It will be less than this 
either if water is in excess, or if there is too little water to 
dispose of all the heat which the steam brings into the con- 
denser. 

361. To Start a Compound Engine. — The compound 
engine, having both a non-condensing and a condensing cylin- 
der, requires to be handled in starting according to the princi- 
ples laid down in both the previous paragraphs. It is usual, 
however, to derive in the compound engine an advantage in 
starting which is not present in the single engine. If the two 
cranks are at an angle with each other, which is usual in power- 
house practice, it becomes possible to start the engine, even 
if the first or high-pressure-cylinder stands, with its crank on 
the dead-centre. A valve connecting the receiver of the low- 
pressure cylinder with the steam-pipe will be controlled by a 
valve which will be called the by-pass valve. By opening it, 
boiler-steam is admitted directly to the low-pressure cylinder, 
which will be at its best mechanical advantage if the high- 
pressure crank is at its dead-centre, and by these means the 
engine can always be started either as a low*pressure or as a 
high-pressure according to the position of the cranks. The 
complication of the steam-heated receiver and steam-jackets 
adds nothing of difficulty to an engine of this sort. The 
jackets make it unnecessary to pay special attention to the 
heating of the cylinder, since to open steam on the jackets 
will accomplish this purpose. Some recent practice has 
attached the steam-pipe of the independent air-pump to the 



MANAGEMENT AND RUNNING OF ENGINES. 649 

jackets and receiver-circuits, so that the steam must be turned 
on to the jackets for warming the main cylinder before the 
engine is started. This is desirable to guard against the possi- 
bility of difficulty caused by unequal expansion of parts which 
are hot and cold. 

The compound locomotive with intercepting- valve operat- 
ing automatically starts just like the simple engine non-con- 
densing. 

In large vertical engines such as are used in marine prac- 
tice, where the engine is on different levels, it is often necessary 
to have several hands for proper starting. Usually one level 
is the working platform in such cases. The common practice 
on board ship is that the chief in starting is at the throttle- 
valve, the first assistant in charge of the valve-gear, and while 
the second is in charge of the fire-room, the third or junior 
will take the bell or signalling apparatus from the bridge, 

362. Lubrication of the Engine. — The bearing-surfaces of 
all parts of the engine require to be separated from actual 
metallic contact by a thin film of some lubricating material. 
This is true both of the moving parts within the valve-chest 
and cylinder and of the external bearings of the mechanism. 
The old practice for lubricating within the steam parts of the 
engine was to introduce tallow, whose body prevented it from 
being dissipated too rapidly under the conditions of heat and 
pressure. The difficulties referred to under paragraph 342 
have made it much more common to use the mineral oils for 
this purpose. The requirements of a satisfactory lubricant are 
that it should have a low coefficient of friction, which means 
that it should not be too viscid or have too high a resistance 
to motion of its particles. It should not be so fluid or limpid 
as to be squeezed out by the contact-pressure of the two sur- 
faces, and it should be without deleterious effect on the sur- 
faces which it lubricates. 

363. Lubrication of Cylinder and Valves. — The lubricant 
required within the valve-chest and cylinder must be intro- 
duced against the pressure prevailing therein. This can be 

I done in one of several ways. 



650 MECHANICAL ENGINEERING OF POWER PLANTS. 

(i) In condensing engines a simple open cup, closed at the 
bottom with a valve or cock, can be screwed into the clear- 
ance of the cylinder, and opened when the pressure in the 




cylinder is less than atmospheric. This is particularly appli- 
cable to vertical cylinders, but will not lubricate the valve. 

(2) The oil can be forced into a cylinder by a pump either 
operated by hand or driven by the engine, or in large engines 
by a small steam-cylinder. If driven continuously by the 
engine or by an independent oil-pump, the feeding of oil is 



MANAGEMENT AND RUNNING OF ENGINES, 651 

continuous and economical (Fig, 503). If driven by hand^ 
the supply is intermittent. 

(3) The modern method of lubrication which prevails most 
widely is the delivery of oil by drops continuously into the 
steam-pipe, using a column of water as a source of power. 
The oil is contained in a closed cup from which two connec- 
tions enter the steam-pipe (Fig. 504). Upon the short one^ 




""^^ 




Fig. 504, 

Ki close to the cup steam-pressure in the pipe is acting, 
while upon the other, F^ connected to the steam-pipe at 
some distance above the cup, both the same steam-pressure 
and the weight of a column of water condensed In that longer 
connection are acting. This column of water displaces the oil 
at a controlled rate into the surfaces to be lubricated. Its 
action is continuous. 

(4) What is called the oil-cup or cylinder-cup is a brass 
vessel with a pipe-connection from its bottom, in which is a 
valve. The cup has a lid at the top which is screwed on and 
steam-tight. When the valve in the bottom is closed the oil- 
cup is cut off from the cylinder and the lid can be lifted off 
and the cup filled. When the lid is in place the lower valve 



652 MECHANICAL ENGINEERING OF POWER PLANTS, 

can be opened, and the pressure, equalizing, will permit the 
lubricating material to descend into the cylinder either slowly 
or fast according as the valve-opening may permit. This is 
the air-lock principle, but the feeding by it is intermittent. 

364. Graphite as a Lubricant. — The objection to oiling 
cylinders with fluid oils in condensing engines is the difficulty 
from the oil in the exhaust and in the boiler (par. 197). 
Graphite possesses a lubricating quality, has a low coefficient 
of friction, a body which prevents it from being forced out 
of the surfaces where it should act, and furthermore seems to 
iill the pores of the surfaces so that they acquire a singularly 
smooth and mirror-like surface where it has been used. It is 
introduced either as a powder or in combination with some 
other lubricating material as a vehicle. 

365. Lubrication of Bearings. — The bearings in a steam- 
engine which require to be lubricated are those of the shaft 
eccentric-straps, the crank-pin, and the cross-head pin and 
guides. The main-shaft bearings are the only ones which are 
stationary so as to be reached by the ordinary hand methods, 
and the convenient and automatic lubrication of all bearing's 
lias brought the application of many devices to maintain a con- 
tinuous and abundant supply of oil. What are called sight- 
feed oil-cups are those in which a supply of oil is held in the 
cup and is allowed to drip from its bottom through a valve 
which controls the opening in such a way that the size and 
number of drops can be seen and regulated (Fig. 505). The 
oil from such cups falls through pipes which conduct it to the 
fixed bearings, where they are distributed by proper grooves cut 
in the bearing by which the motion of the shaft makes the oil 
spread where required. The connecting-rod bearings are the 
most difficult to provide for, because it is a secondary piece 
supported upon two other moving pieces. The crank-pin is 
lubricated either by centrifugal force as shown in Fig. 506, 
whereby oil received near the centre of motion is carried 
outward through a pipe to the centre of the pin, and is there 
distributed through a radial hole outwards upon the bearing- 
surface, or else a flat piece of metal is brought against a 



MANAGEMENT AND RUNNING OF ENGINES. 



655 



webbing by the oscillation of the connecting-rod, and wipes 
the excess of oil off the webbing so that it is delivered down- 




Fig. 505. 

wards upon the pin (Fig. 507). For the cross-head pin a 
similar fixed cup is placed over the path of the cross-head 
having on its under side a piece of webbing or similar textile 
material upon which the oil drops and is spread. Illustrations 



^54 MECHANICAL ENGINEERING OF POWER PLANTS. 

of these methods of lubricating will be seen in the various 
types of engines hitherto presented. 




Fig. ^o6. 




Fig. 507. ^ 

In large engines with many cylinders and multiple mechan- 
isms a practice has been followed of bringing all oil-cups to a 



MANAGEMENT AND RUNNING OF ENGINES. 



655 



few points and connecting these oil-cups by pipes to the 
various bearing-surfaces to be lubricated. In vertical engines 
of the marine type it is usual to lubricate the crank-pin 
by means of a pipe running along the connecting-rod, and 
ending near the tross-head pin in a flaring mouth into which 
the sight-feed oil-cup shall deliver its oil and from which the 
pipe shall carry it to the pin. It will be apparent that, as 
the cross-head travels in a straight line, the mouthpiece will 
always be under the end of the oil-cup in all positions. Bear- 
ings have also been made self-lubricating by means of rings 
which turn in a bath of oil below the bearing, and rest upon 
the shaft to which they are internally tangent. As these 
rings revolve with the shaft, the oil which adheres to them is 




Fig. 508. 

continuously brought up from the reservoir and delivered at 
the top of the shaft from which it is distributed. 

Siphons of lamp-wick have also been used as a means of 
securing a continuous slow feed from an oil-cup. The oil 
rises by capillary action in the wick, and when it has reached 
the bend in the tube within the cup in which the wick is 



656 MECHANICAL ENGINEERING OF POWER PLANTS. 

placed it descends by gravity down the linger arm and is 
delivered in drops in the bearing below. (See Fig. 262). 

Greases are another form of lubricant whose delivery from 
a reservoir can be secured by the slight rise of temperature 
from friction causing the vessel containing the grease to 
become warm and some of the grease to melt and run down 
through holes in its bottom. As the temperature falls the 
grease ceases to flow. Grease-cups have also been used in 
which a more resistant viscid grease is forced through the 
delivery-opening by the pressure of a spring controlled by a 
screw and nut (Fig. 508). This is particularly convenient for 
lubrication of locomotive-rods, where it is desirable that the 
oil-cup should be closed from grit and dirt, and where the 
methods of the stationary plant cannot be applied. 

366. Tests of Lubricants. — The subject of the various 
lubricants is too broad a one to receive full treatment under 
present conditions, but brief reference may be made to three 
important tests. An oil is liable to fail of its purpose when 
for any reason it is prone to oxidize from heat or use and 
to become gummy as the result of that chemical change. 
Gumminess is a relative quality, and consequently the test 
to determine this is a relative test between the most limpid 
and the most readily oxidizable of the oils. The test for the 
gumming quality of the oil is to drop a certain weight or 
volume of the oil to be tested in the middle groove of three 
made upon a surface of cast iron which is inclined to the 
horizon at a slight angle.* In one of the other grooves is 
dropped an equal weight or volume of sperm-oil, which has no 
tendency to gum, and in the third an equal weight or volume 
of linseed-oil, whose gumming qualities are so great that it is 
used as a drying oil. The three oils slowly run down the 
grooves, undergoing oxidation and becoming more and more 
sluggish as they flow. The distance covered by the oil to be 



* One foot elevation in six of length if the oil is to be tested in ordinary air.. 
If the slab is heated, the slope may be steeper, and the test will require less time 



MANAGEMENT AND RUNNING OF ENGINES. 657 

tested, as compared with the distance covered by an oil hav- 
ing the greatest and least quality of gumming as represented 
in the other two, measures its excellence in this respect. 

The test for acid in an oil is made by putting a small 
quantity of the oil in a test-tube with a little copper scale of 
the suboxide of copper, Cu^O. If there are fatty acids 
present, after some hours' exposure and with gentle heat the 
reactions with the copper turn the solution green. If the oil 
has a vegetable acid, it will turn blue. Further qualities of 
oils for lubricating purposes are determined by their low fire- 
point. If they give off an inflammable vapor by heat, they 
are of course a dangerous element. 

367. Accidents in the Engine-room. — It would be impos- 
sible to discuss all possible accidents to all kinds of engines 
in the limited space permitted here. The most usual thing 
which goes wrong is the overheating of a bearing, either from 
too tight fitting of the bearings (Chapter XVI), or by defec- 
tive alignment (Chapter XIV), or from the use of poor oil or 
too little of it. The hot bearing is first annoying from the 
excess of friction which it indicates, but after a short period 
of heating the parts expand, increasing the friction or hold 
which they form upon each other, whereupon the contact- 
surfaces begin to cut each other and the presence of the 
abraded material caused by such cutting occasions greater 
heating and finally destroys the contact-surfaces so that until 
refitted they will never run cool. For a revolving bearing 
which heats only moderately a wick or mat of some fibrous 
material which dips into a bucket of water can be used upon 
the heating shaft. Most marine engines (where alignment 
is troublesome by reason of the flexibility of the hull which 
carries the bearings) are fitted v/ith special arrangements for 
carrying a current of water to be discharged upon the bearings 
and keep them cool. When cutting has begun it can some- 
times be arrested by using a lubricant of heavier body, or by 
compounding a lubricant by mixing tallow and graphite. If 
the bearing is very large and the cutting very serious, a 



658 MECHANICAL ENGINEERING OF POWER PLANTS, 

mixture of tallow with lead-filings and powdered sulphur 
makes a compound which fills up the abraded surface in part, 
and often has prevented the cutting from going further until 
the bearings can be permanently refitted. Mercury may take 
the place of the lead. 

In an engine otherwise well designed heating may be due 
also to the concentration of the load upon too small an 
area. This is incurable as a fault in design, but the heating 
which has been referred to above is the type which is pre- 
ventable. 

An engine may give trouble by a knock or pound at some 
part of its stroke. Probable causes for this knock or pound 
are: 

(i) The main shaft out of line, so that the crank-pin is not 
perpendicular to the cylinder-axis. 

(2) Lost motion in the pin-joints. 

(3) Lost motion of the piston-follower, or of the entire 
piston on its rod by reason of the slacking of the nuts or keys. 

(4) The valve loose on its rod or within its yoke. 

(5) A shoulder in the cylinder, worn in the bore, which 
some change in the length of the mechanism causes the piston 
to strike. 

(6) A side motion of the piston forced against the side of 
the bore when the steam comes on a piston which overlaps the 
port. 

(7) An up-and-down motion of the piston toward the 
middle of its stroke by a deflection of the guides under the 
oblique pressure from the connecting-rod. 

(8) A loose guide, or the cross-head does not have full 
contact against the guide at all points. 

(9) Defective proportion of the steam-pressure to the 
weight of the reciprocating parts, so that the effort of the 
steam does not reach the crank-pin until after the latter have 
been accelerated. Delayed admission of steam produces the 
same effect. 

(\6) Improper compression, so that the lost motion neces- 



MANAGEMENT AND RUNNING OF ENGINES, 659 

sary in the bearings for lubrication takes up upon the crank- 
pin instead of upon a steam-cushion in the cylinder. Ex- 
cessive compression may lift the valve, whereby a knock 
occurs when the valve returns to its seat. 

The renewing of packing in stufifing-boxes of rods and 
stems is scarcely to be considered under the head of an 
accident, but belongs rather to the general maintenance of an 
■engine in its proper working condition (Chapter XV). 



CHAPTER XXX. 
TESTING OF THE POWER PLANT FOR EFFICIENCY. 

368. General. — The testing of the power plant belongs to 
a department which has been called experimental engineering 
and whose practitioners have been called steam experts. It 
forms a field too large to receive more than general allusion 
in a treatise such as this. The object in any power plant 
will be to ascertain whether the energy supplied in the form 
of fuel and liberated as heat in the furnace is being utilized 
as well as it might be, and with as great economy as pos- 
sible; and further, to find, if such is not the case, at what 
points improvement and elevation of standard are to be 
sought. In a plant consisting of engine and boiler or a num- 
ber of both it is obvious that there is an efficiency of the 
plant as a whole, and there is an efficiency of the boiler and 
efficiency of the engine separately. Such questions also 
come to the manager in control of a power plant when new 
appliances which are called improvements are presented for 
adoption. It is undoubtedly a stimulus to the operators of 
a power plant to know that at certain convenient intervals 
the efficiency of the plant is to be observed by the conduct of 
proper tests. 

369. The Boiler-test. — The boiler-test is usually con- 
ducted to find out how much water is evaporated in the 
boilers for each pound of coal burned in the furnace. This 
involves weighing the water supplied to the boiler through the 
feed-pump in a given time, and the coal charged during that 
same time. The ash and incombustible matter withdrawn 
from the ash-pits are to be subtracted from the coal burned 
as a means of finding out the percentage of ash and crediting 
the boiler with the actual combustible supplied to it, and the 

660 



TESTING OF THE POWER PLANT FOR EFFICIENCY. 66 1 

steam passing off through the steam-pipe should be sampled 
at frequent intervals during the test to see whether it is 
delivering evaporated water in the form of steam, or is 
entraining water through the pipe of the engine without form- 
ing steam. It is obvious that to refrain from this check upon 
the quality of steam is to credit the boiler with evaporating 
more water and disposing of more heat than it actually did, 
and therefore to increase in the result the amount of water 
really and effectively handled by the boiler in a given time. 
The weight of coal charged into the furnace is determined by 
scales of any reliable structure which will read to a quarter of 
a pound, and the weight of water by having two tanks 
similarly mounted on scales into which the suction-pipe of 
the pump can be placed alternately, and the weight of water 
fed determined by the difference between the initial and final 
readings as each tank is alternately filled and emptied. It is 
usual to have an observer specially detailed for the coal and 
the water scales, with blanks upon which he makes the entries 
as observed and which form the log of the test. Meters 
may be used to check the weighings. 

370. Flue-gases. — It is desirable in a boiler-test to know 
whether the products of combustion escaping from the setting 
are carrying an unnecessary amount of heat to waste, and 
whether the furnace-gases are of proper constitution with 
respect to waste of fuel in them or excess of oxygen reducing 
the temperature in the furnace. The temperature of the i^ue- 
gases can be observed by a standard pyrometer, if such are 
at hand ; or a very close result can be obtained by the method 
with a ball or mass of iron inserted in the flue until it acquires 
the temperature of the gases, and then cooled in a known 
weight of water whose rise of temperature in cooling the mass 
of iron is observed (see Notes). The volume of the flue-gases 
or the weight of the products of combustion can be ascer- 
tained from the readings of a gauge introduced so as to de- 
termine the difference of pressure within the flue and outside 
of it. The composition of the chimney-gases is determined 
by gas-analysis methods, the best known apparatus being 



662 MECHANICAL ENGINEERING OF POWER PLANTS, 

that of D'Orsat. Such appliances are specially directed to 
determine the amount of carbonic oxide, carbonic acid, and 
oxygen. 

Coal-calorimeters for observing the calorific power of the 
fuel have already been referred to in paragraph 287. 

371. The Calorimeter. — There are several forms of calo- 
rimeter which are used to determine the quality of the steam 
or the percentage of moisture which it contains, in order to 
correct the record of the scales which weigh the feed-water. 
These instruments withdraw from the main steam-pipe a 
sample of the steam which is passing through it, by means of 
a nipple which crosses the pipe and suitable perforations in it 
withdraw the material which is passing through the pipe at all 
its sections. The material drawn out through such a nipple 
is- then analyzed by the calorimeter proper of which there are 
many forms. 

The most accepted of current practice is a combined sep- 
arating and throttling calorimeter, in which the water in the 
sample taken from the pipe is first separated, and then the 
steam analyzed by passing it through a throttle orifice whereby 
it becomes superheated. The heat necessary for evaporating 
the water which it contains is measured by the difference in 
reading of thermometers inserted into the instrument. Other 
types of calorimeters are the coil-calorimeter, in which the 
determination of the percentage of moisture is based upon 
the amount of heat necessary to condense the mixture which 
passes through a coil, and the barrel-calorimeter, in which a 
sample of the mixture from the nipple is taken into a barrel 
of water through a flexible hose for similar condensation. 
The determinations are made by observing the difference in 
the heat-units required to condense the mixture as compared 
with what would be required if it was altogether steam. 

372. Report of a Boiler-test. — The importance of a 
reasonably close agreement in methods for the conduct of a 
boiler-test have induced engineers to attempt to agree upon 
such standard methods, and a uniform method of tabulating 
and reporting them, together with the calculations which are 



TESTING OF THE POWER PLANT FOR EFFICIENCY. 663 

involved in making the deductions from a boiler-test. The 
headings of such a standard form of report will be found in 
the Appendix. 

373. The Engine-test. — It has already been made ap- 
parent (pars. 6 and 7) that for many engines the resistance 
appears in a form in which it can be directly measured so as 
to determine the net or effective work received from the 
engine. Such cases would be where the work of the engine is 
pumping or hoisting, or the generation of electric energy. In 
many cases, however, where the resistance of the engine con- 
sists in driving the transmissive machinery of large establish- 
ments, the net resistance is not directly measurable, and the 
only method of determining the power and work of the engine 
is by means of measurements made upon the effort in the 
cylinder. Moreover, under many circumstances the insertion 
of the measuring apparatus between the motor engine and the 
net resistance would be inconvenient or impossible. This 
limitation of direct measurement is often imposed by the 
magnitude of the units involved, if for no other reason. If 
the power is small enough to be conveniently determined by 
direct measurement, the apparatus used for this purpose will 
be called a dynamometer. If the work is to be measured in 
the engine-cylinder, the instrument used will be called an 
indicator. 

374. The Dynamometer. — The function of the dynamom- 
eter is to measure the effort passing through it by giving the 
pounds which constitute that effort multiplied by the space in 
feet through which it moves. The dynamometers often are 
adapted to make only the observation of the effort in pounds, 
leaving the space passed over to be otherwise observed. 
They are of two great classes. If the effort is absorbed in 
the dynamometer and does not pass beyond it, it will be 
called an absorption dynamometer. If the effort passes 
through the apparatus to a resistance beyond it, to which it 
is transmitted so as to undergo measurement, but no absorp- 
tion beyond the friction or tare of the instrument, it will be 
called a transmitting dynamometer. They may each be 



664 MECHANICAL ENGINEERING OF POWER PLANTS. 

further subdivided according to the methods of transmission 
and of absorption. The absorption dynamometer usually 
absorbs by friction the work transmitted to it applying the 
principle of a brake, which exerts a tendency to hold its 
brake-wheel from moving, and the effort to resist its motion 
expressed in pounds and multiplied by the feet through which 
that resistance passes gives the foot-pounds or horse-power. 
The heat of friction must be disposed of by cooling appliances, 
and in many forms the variation in the coefficient of friction 
between the brake-wheel and its shoes makes the use of this 
means a somewhat delicate operation. In the transmitting 
dynamometer involving rotary motion the usual plan is to 
drive the resistance through a spring which is attached to the 
end of a convenient lever on the driving and driven parts of 
the apparatus. The separation of the driving lever from the 
driven lever indicates the tension or compression upon the 
measuring spring, and thus the power in pounds is observed 
by noting the condition of the spring and the speed at which 
the effort is moving. Such dynamometers are usually re- 
stricted to comparatively small powers. Other types deter- 
mine the power transmitted by belting, by measuring the 
tensions upon the two bights of the belt, or by weighing the 
effort required to equate the pressure upon bearings, and for 
small sizes floating dynamometers have been successfully used 
in which the effort necessary to keep a tank or vessel upon an 
even keel when floating upon a surface of water measures the 
tendency to turn it, and therefore determines the power which 
is passing through the apparatus borne upon such tank or 
vessel. 

These methods are of comparatively narrow application to 
power plants of large size, and for their detailed application 
reference should be had to special treatises upon this subject. 

375. The Indicator. — For the observation of an effort 
exerted upon the piston of an engine, a device for measuring 
or observing the intensity of the pressure upon such piston at 
every point of its stroke becomes necessary. Such an appa- 
ratus was worked out by James Watt, and was by him called 



TESTING OF THE POWER PLANT FOR EFFICIENCY. 66$ 

an indicator. The diagram of effort which has been used 
throughout this work (Chapters III and VI) is really the 
diagram which is given experimentally by such indicator. It 
consists of a piston of known area moving with the least 
possible friction in a little cylinder, whose under side is in 
communication through as short pipe-connections as possible 
Avith the end of the cylinder. It is usual to make this con- 
nection into the clearance, but at such point that the flow of 
steam through the ports shall not affect the pressure actually 
prevailing where the indicator is connected. This pressure 
connected on the under side of the indicator-piston would 
force it upwards in its cylinder, and this tendency is resisted 
by a spring carefully calibrated with respect to the area of the 
piston, so that it shall undergo certain definite deformation 
under certain definite pressure. It will be apparent then that 
the deformation of this spring will weigh the pressure, and if 
a tracing-point or pencil be attached to the piston, it will 
draw a curve which will be the ends of ordinates correspond- 
ing to the pressure on the indicating piston in terms of the 
scale of the spring. If a motion of a paper at right angles to 
the piston motion be provided, a closed curve will be made, 
which will thus record the pressures in the cylinder at every 
point of the stroke, if the movement of the paper be pro- 
duced by a linkage or mechanism driven from the piston by 
a positive reducing connection. It is usual to reel the paper 
of the diagram upon a barrel which is rotated through a part 
of a revolution by a reducing mechanism driven from the 
engine cross-head. 

It will be apparent that with a known scale of spring in 
the indicator the mean height of the diagram which it traces 
will be the mean pressure upon the piston. The mean height 
can either be ascertained by finding the area of a diagram 
with a planimeter and dividing that area by the length of the 
diagram, or the mean height of the diagram can be observed 
by dividing the length of the diagram into equal parts, and 
measuring the height in each segment, adding their aggregate 
together and dividing by the number of heights measured. 



666 MECHANICAL ENGINEERING OF POiVER PLANTS, 

It will be further apparent that the lines of the diagram 
will indicate the satisfactory working of the distributing- valves^ 
or the reverse, by reason of the relation of actual pressures to 
those which ought to prevail, and furthermore the approxi- 
mation of the curves of effort to those which theory indicates 
as desirable. The indicator is thus a check on the setting of 
the valves, sizes of ports, friction through pipes, resistance to 
free release of exhaust, excessive condensation, ill-adjusted 
expansion, and the like. 

The errors of the indicator are those due to defective 
accuracy of springs, inertia in the moving parts, which causes 
them to move further than simply to balance the pressure, 
friction which prevents their moving as far as they ought to- 
balance the pressure, and inaccuracy in the reproduction on 
the diagram of the motion of the piston in its true relation by 
reason of defects in the mechanism used to give motion to the 
paper. 

376. Deductions from the Indicator-card. — The primary^ 
deduction from an indicator-card is the mean effective pressure 
(usually called M.E.P.) as measured directly from the card. 
The diagram can, however, furthermore be used for a more 
important purpose, which is to determine the volume of 
steam for each stroke, and hence to infer the weight of water 
used in the development of a horse-power. The volume and 
pressure prevailing in the cylinder at the completion of its 
stroke, or when exhaust takes place, enables the volume and 
weight of steam, and therefore of water, to be calculated 
when it is assumed or known that the steam at the release 
into the exhaust-pipe was dry and saturated, which it is 
likely to be. 

This is not the full quantity of steam which works through 
the engine, because the indicator does not take account 
necessarily of all water resulting from condensation. It is 
more accurate to use the volume at release than at the cut-off 
point, which might otherwise be equally well used, by reason 
of the fact that at cut-off less water has been evaporated than 
will be given at the reduced pressure which prevails at the 



\ 



TESTING OF THE POWER PLANT FOR EFFICIENCY. 66/ 

end in an expanding engine. An indication of the presence 
of evaporated water will be given by the diagram when the 
curve indicating the relation of pressures during expansioa 
passes unduly outside of the theoretical curve of such expan- 
sion. This indicates that water has been evaporated which 
has raised the pressure in the cylinder, but has done it at the 
expense of the heat of its walls. 

The difference between the indicated horse-power and the 
net or effective horse-power of the engine will be caused by 
its own friction as a machine involving the resistance offered 
in the cylinder, at the valves, at the stuffing-boxes, at the 
pins, guides, and bearings. This quantity is apt to be a. 
nearly constant resistance even under quite wide variations of 
load, and can be observed, if circumstances permit, by taking^ 
an indicator-card when the only resistance upon the engine at 
the given or desired speed is its own friction. The foot- 
pounds given by that observation is the friction of the engine, 
and is to be subtracted from the indicated horse-power to give 
the net or effective horse-power. 



CHAPTER XXXI. 
GENERAL REMARKS UPON THE POWER PLANT. 

377. Concentrated or Subdivided Steam-power. — There 
are two policies possible in the design of a power plant where 
the resistance to be overcome is extended over a large 
number of units, tools, machines, or whatever. The power 
may be liberated from the fuel in a central location and 
transformed into motor energy in a large engine near the boiler 
plant, and from this large engine, power may be transmitted 
by shafting and belting all over the plant for use as required. 
The other plan is to carry the power in the form of steam to 
a large number of small steam-engines located at convenient 
points and each of which drives its own section or group of 
machines. 

There is no question as to the wisdom of concentrating 
the generating or power-furnace plant, whichever of the other 
two systems be considered advisable. The reason for this is 
that the handling of fuel and of ashes and superintendence of 
the boiler plant is made economical in proportion as the num- 
ber of these units is large when they are concentrated under 
one superintendence and in one place. The fire-risk and in- 
surance problem is also diminished by the scheme of concen- 
tration. It becomes of advantage to use mechanical methods 
for handling fuel where large numbers of horse-power are 
concentrated and where one mechanical plant can serve for 
them all. The cost of stack or artificial-blast appliance is less 
per unit when they are together. 

Much the same arguments are to be urged for the princi- 
ple of driving the plant from one central engine. The con- 

668 



GENERAL REMARKS UPON THE POWER PLAN7\ 66(^ 

centration of supplies, repairs, and superintendence, which 
will vary with the number of engines and not with their size, 
all point to the advantage of this system, as in the case of the 
boiler plant. There is the further advantage that the large 
engine will be more economical in proportion than the indi- 
vidual small ones, furnishing in the aggregate the same 
amount of horse-power. This is one of the arguments for 
the central-station method of furnishing power for street-rail- 
way propulsion rather than by individual motors. With the 
central engine the loss in transmitting its power by shafting, 
belting, or sirriilar means to the individual and subdivided 
machines is a loss in friction; and furthermore, with some 
exceptions it will be necessary to drive the whole plant of 
transmissive machinery in order to run a small section of it for 
work overtime or where it must not be intermitted, as in the 
boring of cylinders and such work. Moreover, the failure of 
the central engine or any part of the transmission machinery 
makes it necessar}'' to stop the entire establishment. With 
subdivided power only the part affected need be isolated for 
repair, while the rest runs on without interruption. 

With the system of subdivided power among small engines 
the transmission loss is from condensation of steam in the 
pipes which connect the boiler plant to the various engines, 
which is probably, with an efficient system of non-conducting 
coverings (Chapter XVIII), less than the loss by friction 
expressed in percentage of the whole power furnished to the 
piping system. This plan furthermore has the advantage 
that only the section of the plant which is desired need be 
run for overtime or special work, and the system is further 
flexible if it is desired to run one engine with its attached 
machinery at higher speed or slower than the normal. The 
aggregate first cost of the number of engines, if cf the same 
character as to workmanship as the single large engine, when 
the cost of foundations and pipe and of drip and exhaust 
connections is added, is likely to exceed the first cost of 
the large engine. On the other hand, the whole power for 
the plant does not have to pass through the first set of trans- 



670 MECHANICAL ENGINEERING OF POWER PLANTS. 

iniss-ive shafting, but the principle of subdivision enables each 
section of shafting and its corresponding pulleys to be lighter 
in proportion, diminishing the friction which is caused by 
weight, and failure of one engine or main belt does not arrest 
the whole plant. 

378. Distribution of Power by Electricity, Gas, or Air. 
— In addition to the methods of transmitting power by steam 
or shafting discussed above, the methods of distributing by 
other transmission systems should be considered. The first 
plan is that of using an electric generator in connection with 
the central engine from which the power will be distributed by 
wires carrying the current to the sections driven each by its 
own independent motor, or to separate machines each with its 
own motor. The cleanliness, convenience, compactness, and 
easy control of the electric transmission makes it very attrac- 
tive, and the loss in the conversion of the steam energy into 
electric energy and its transmission and reconversion into mo- 
tion are apt to be about the same as the losses in friction in 
high-grade plants, and will be less than such losses where set- 
tling or careless management has permitted the transmissive 
machinery to deteriorate in quality. If but one generator is 
used, there is the same difficulty as with the central engine in 
the previous paragraph, that a breakdown of that central engine 
stops the entire plant; but this can be met by either duplicate 
engines, or by the principle of subdivision in the power house, 
where the aggregate of several units makes up the entire 
source of energy, and they are not likely to fail all at once. 
The expense of multiplying motors must be considered in this 
system, although it must not be forgotten that with it the 
cost of shafting, hangers, and pulleys does not have to be 
incurred, and serves to off^eet the cost of motors. 

Until the commercial problem of the storage of electrical 
energy shall have been successfully solved, electrical trans- 
mission systems offer the same objections which belong to 
the preceding plans, that there is no storage of energy when 
not wanted, to be given out when it is called for. This is a 
great advantage which is offered by the use of gas-engines 



GENERAL REMARKS UPON THE POWER PLANT. 6^1 

operated by gas made in a producer and stored in a holder. 
The gas-engine operates only when wanted, and when gas is 
shut off from it all expense connected with it stops except 
interest. Gas can be made at maximum efficiency for a 
short period, and then the expense connected with its genera- 
tion stops until the supply is exhausted. The system possesses 
all the other advantages of subdivided power. 

The distributing of power by compressed air for motors 
has not been widely extended by reason of the usual absence 
of any conditions which make the use of the exhaust-air 
convenient or desirable at the place where it is discharged. 
In mining practice and similar places this is an immense 
advantage for compressed-air machinery, which is furthermore 
<:lean and convenient. There is a loss in the double conver- 
sion at the air-compressor in the power house, and the 
reconversion at the air-engine, which is only to be offset by 
the use of extra heating appliances at the motor whose cost 
i«ust be charged to the method of transmission. This in no 
way is to be considered as an argument against the conven- 
ience of compressed air for many machines of the portable or 
detached character. 

379. Location of a Power Plant. — The choice of a loca- 
tion for a power plant is often fixed by considerations over 
which the engineer has no control. When such control is 
possible the considerations directing the choice of a location 
are mainly those of good sense and experience with respect 
to some of the following points: 

(i) It must be accessible for the delivery of the fuel- 
supply and for the removal of ashes. In cities with a water- 
front so that coal can be carried directly into the storage-bins 
from boats a considerable saving in cost per ton is to be 
effected, and this points to the selection of such water-front 
when otherwise convenient and possible. In the absence of 
water-transportation, the railway and the possibility of use of 
sidings from it are important features. It has already been 
discussed (Chapter XXIV) that the delivery of coal into a 
boiler-room by gravity diminishes the cost of a plant, but the 



672 MECHANICAL ENGINEERING OF POWER PLANTS. 

fuel can as well be elevated within the power plant as without 
it. In cities where the transportation within the streets majr 
be interrupted by the winter snows it is important that a 
sufficient storage capacity should be supplied in the plant to 
prevent possibilities of stoppage if there should be any inter- 
ruption of regular transportation. 

(2) The water supplied to a power plant is a vital ques- 
tion, and a disregard of it in advance has often increased the 
operating expenses considerably. In most cities the water 
for a power plant is metered from the city or water company's 
mains, so that a fixed charge per annum for water is an 
element which must be considered. If condensation is to be 
effected, a supply of water for this purpose is also required, 
and in a large plant it becomes a very considerable quantity. 
It is quite usual to obtain this water of condensation from wells 
sunk within the grounds of a power plant, and a nearness to 
large bodies of water in streams or rivers is of manifest advan- 
tage in this respect. It is often found that well-water either 
from deep artesian wells or the driven-well sources is apt to 
contain matter deleterious to boilers, rendering such water 
unfit for steam-making. References to methods for saying 
water used in condensation have been given in Chapter IV. 

(3) Proximity to the water-front or the railway often 
favors the third element in selecting a location, which is to find 
a place where the smoke from the furnaces discharged through 
the chimneys shall not make the power plant a nuisance in the 
view of the neighborhood. The large chimney-stacks, if that 
method of draft is chosen, are useful rather than ornamental 
outside of the industrial district of cities; and if by the use of 
artificial draft or from the nature of the power plant (pars. 284 
to 286) there is noise within it or an unpleasant vibration 
caused by the engine exhausts or other reciprocating motion, 
it may ^\w^ rise to obstacles, legal and otherwise, to the satis- 
factory operation of the plant. 

(4) The securing of draft from the chimney-stack, if 
natural draft is used, must be sought by locating the stacks 
in such a relation that surrounding conditions shall not pre- 



I 



GENERAL REMARKS UPON THE POWER PLANT. 673 

vent their satisfactory working. High buildings either in 
the line of prevailing winds to windward or to leeward of a 
stack will make conditions unfavorable to it. 

(5) The cost of the ground is also likely to be affected by 
the location chosen with regard to the previous conditions^ 
but in their absence it cannot be disregarded. It is usually 
to be foreseen that the power plant will grow with the 
increased demands which are likely to be put upon it, and the 
obtaining of the necessary land for such growth is a matter to 
be considered to some extent in location. 

380. Construction of a Power House. — The construction 
of a power house will be conditioned very largely by the price 
of land and the ground which it may be allowed to cover. If 
ground is not expensive, there are great advantages in making 
the power plant all on the ground-level, both engines and 
boilers. It is desirable not to put them in the same room 
with no separating partition, by reason of the heat and dust 
which the fires cause, and the moisture in the air which 
comes from leakage and evaporation. If the boilers and 
engines must be under one roof, a separating partition with 
as few door-openings as possible is necessary. It is desirable 
on account of fire-danger to keep the engines and boilers 
within separate fire-walls. 

If ground is too costly to permit this arrangement, the 
boilers and engines must be arranged vertically in successive 
stories, and it becomes a question whether to put the great 
weight of the stationary boilers on the ground or in a base- 
ment, and the lighter weight, but moving masses, in the upper 
layers, or to reverse this arrangement. The older plan was to 
put the boilers and coal below, and the engines above. It is 
interesting to observe the reversal of this system in some 
modern power plants in the larger cities where ground must 
be economized. The revolving machinery is put in the 
basement on the ground, where its vibration can produce the 
least effect upon the walls and floors. The dead load of the 
boilers and their contents is borne upon the next tier of floors, 
and the coal-bins are put at the top of all with elevators or 



674 MECHANICAL ENGINEERING OF POWER PLANTS. 

hoists to fill them conveniently from the street-levels. This 
offers manifest advantages in economy of handling material, 
and the only objection to be urged is the slightly diminished 
effective height of chimney which is caused by elevating the 
boilers. 

The construction of the power house will be conditioned' 
somewhat by the foregoing principles. If it is a single-story 
building, the ordinary construction of brick walls with proper 
foundations and a light iron roof is the typical and approved 
design. It is, however, exceedingly convenient in the power 
plant to have it commanded by a travelling crane spanning 
from wall to wall, so that the rapid handling of machinery in 
case of repair or substitution or extension is possible with such 
facilities. In the two-story or many-storied power plant the 
construction becomes the more costly, by reason of the 
weight to be provided for per square foot of floor-space, and 
of the necessity for fire-proof construction and of the weights 
which come upon the walls. This opens a department of the 
subject with which the present limits of subject and space 
make it impossible to cope, and which belong to the depart- 
ment of the structural engineer. In such a building the pro- 
vision for growth by addition of engine-units is to be foreseen 
and provided for, since the limitations imposed by the wall- 
construction are positive and fixed, 

381. Arrangement of the Power Plant. — It is a conceded 
principle of power-house practice for public use that the 
machines must be in whole or in part in duplicate, so that the 
failure of any part shall not necessitate an entire stoppage of 
the supply of power to users. If, therefore, the duplication 
is only partial, the failure of some detail in those departments 
of which there is but one example may cripple the whole 
plant. It is usual to have spare boilers and spare engines in 
a large plant, but there are many in which there is ywt one 
steam-pipe, and in which a failure or accident to the pipe 
would be as fatal as to the motive machinery itself. Some of 
the best and newest power plants have everything duplicated 
so that there are practically two plants in one. It is an 



1 



GENERAL REMARKS UPON 7 HE POWER PLANT. 675 

advantage if the principle of subdivision in the plant itself is 
carried out to make the power units of different capacity, so 
that when the demand for power varies it may be made by 
running units of different size to their full capacity, which is 
their most economical working. This is better than to have 
large units but partly loaded and running at a disadvantage 
for most of the time. 

Where the plant is to be driven from a single engine by 

j belts and shafting, the engine should be at or near the centre 

of the length of the main line of shafting. This diminishes 

the weight of shafting and friction, because only half as much 

power has to be transmitted by the torsion of each half-length 

I if the resistance is wisely distributed. This plan gives rise 

j to a ground-plan which develops into a capital letter H, the 

! power plant being in the cross-bar between the two buildings. 

;! There are special details of construction belonging to 

^1 power plants which drive electric generators, as to the use of 

iron nails in floors and walls, which belong specifically to that 

department. 

382. Fire Protection of the Power Plant, — The struc- 
tural methods to be observed in power plants with respect 
to danger from fire have been a special study by the insur- 
ance companies. The conditions in general are that whatever 
woodwork there is in the power house should be massive, and 
the least possible space left concealed where the fire might 
start and lurk undetected until it had acquired headway. 
The construction of fire-doors and shutters to prevent the 
passage of fire and flame through walls is also a matter of 
iBome importance. 

383. Floors of the Boiler Plant. — The floors of a machine- 
shop or engine-room are very important features of the builds 
ing. A concrete floor either of the ordinary construction or 
made of some of the proprietary materials is the suitable 
arrangement for the fire-room space where not exposed to 
cracking from heat of ashes and similar condition. It is 
usual to lay down a fire-brick pavement close to the boilers, 
and the hot ashes and clinkers should be kept upon it. 



d'J^ MECHANICAL ENGINEERING OF POWER PLANTS. 

Ordinary brick or flagstone paving-stones will be found in- 
many places where cement or artificial stone is costly or 
inconvenient. It is desirable that the floor should be one on 
which an abundance of water can be used for washing, and 
which should be arranged to drain itself into suitable catch- 
basins and drains by the grades used. A brick or concrete floor 
is not desirable for a room containing machinery, by reason of 
the continual grit which is worn from the floor by treading on 
it, and which currents of air carry into the revolving bearings. 

For the engine-room a wooden floor in two thicknesses is 
quite usual. The standard basement floor of the fire-insurance 
companies is a two-inch plank tongued and grooved, and laid 
on asphaltic concrete, while above that the floor-boards 
proper, ij inches thick, are blind-nailed. For upper floors 
the plank is 3-inch. The upper surface is the part subject to 
injury from weights upon it, and can be removed when worn 
without disturbing the main floor-surfaces. The floor- of an 
engine-room should be of a structure which shall not be 
slippery by reason of oil which may get upon it. In electric- 
power stations wooden floors are of special significance, 
because a brick or cement flooring makes a sufficiently good 
electrical connection with the ground to make accidental con- 
tact with a dynamo dangerous to a man standing on such 
floor, while with wood he is adequately insulated. 

The subject of construction of industrial buildings is too- 
broad a one to be more than hinted at in such a connection 
as the foregoing, and the interested reader is referred to more 
extended discussions for exhaustive treatment. 



APPENDIX. 



HISTORICAL SUMMARY. 

B.C. 120. Hero of Alexandria describes a steam reav^tion-wheel in his 

Spiritalia seu Pneumatica. 
A.D. 1601. Giovanni Battista della Porta in his Pneumatics describes 
condensation of steam in a closed vessel as a means of 
lifting water. 

1615. Solomon de Caus i^Les Raisons des forces Mouvantes) describes 
raising water by steam-pressure above it in a closed 
vessel. 

1629. Branca describes turning a wheel by jet of steam against 
vanes, 

1663. Edward Somerset, second Marquis of Worcester, describes 
in his Century of Inventions a separate boiler whose pres- 
sure was admitted upon water in a closed vessel, 

1680. Denis Papin invents the digester for boiling at high pres- 
sure. 

1680. Huyghens proposes a true cylinder with piston traversing it. 

1681. Denis Papin invents the lever safety-valve. 

1690. Denis Papin applies the piston to receive motor-pressure, 
the cylinder being also the boiler. 

1697. Thos. Savery pumps by forcing water up by pressure and 

lifts water into the chambers by the vacuum caused by 
condensing, 

1698. Savery's first patent for a pumping-engine. 

1705. Papin applies lifted water to turn a rotating wheel. Uses 
internal fire-box boiler. 
1705-07. Thos. Newcomen and John Cawley, with Savery, combine 
separate boiler, cylinder and piston, and surface conden- 
sation. The Atmospheric Engine. 
1716-18. Dr. Desaguliers improves Savery engine by using jet con- 
densation. 
1713. Automatic valve-gear attributed to Humphrey Potter. 
1718. Plug-tree valve-gear for pumps designed by Henry Beigh- 

ton. 
1725. Leupold designs a high-pressure non-condensing engine. 
1730-58. Smeaton improves Newcomen engines. 

677 



678 



APPENDIX. 



1763-64. 

1766. 
1769. 
1781. 

1782. 

1784. 
1799. 
1800. 

1804. 

1804. 

1821. 

1838. 
1840-42. 
1840-45. 

1841. 
1841-44. 



T849. 

1849. 
1854. 
1855. 
1856. 

1857. 

1859. 
1859. 

1859. 

i860. 
i860. 

i860. 
1868. 



James Wait repairs model of Nevvcomen engine at Glasgow 
University. 

William Blakey proposes a water tube boiler. 

Watt's patent of separate condenser. 

Jonathan Hornblowei invents double-cylinder or compound 
engine. 

Watt's patent of expansive working of steam and double- 
acting engine. 

Watt patents parallel motion, governor, and indicator. 

Murdock invents the three-ported slide-valve. 

Trevithick in England and Oliver Evans in America intro- 
duce high-pressure non-condensing engines. 

Arthur Woolf combines two-cylinder engine of Hornblower 
type with higher steam-pressure and Watt's condenser. 

John Stevens designs a sectional boiler. 

Julius Griffith designs a sectional water-tube boiler. 

S. Hall uses a surface condenser on S.S. Wilberforce. 

Stephenson link-motion introduced. 

Shepard & Co. of Buffalo introduce the plug-valve with, 
loose spindle for steam-distribution. 

F. E. Sickles patents a drop or trip cut-ofif. 

Henry R. Worthington invents and introduces direct-acting: 
pumps without fly-wheel and with valve thrown by 
stored energy in springs and by steam-pressure on auxil- 
iary engine-piston : also later the duplex pump. 

Geo. H. Corliss introduces a trip-gear, combined with wrist* 
plate, and plug-valves. 

B-valve designed by Henry R. Worthington for pumps. 

Randolph & Elder introduce compound engine for vessels. 

Greene trip-valve gear introduced. 

Stephen Wilcox uses inclined water-tubes for a boiler. 

Charles T. Porter invents the central-weighted or Porter 
governor. 

Radial valve-gear proposed by Hackworth. 

Independent circulating-pump used for condenser of S.S. 
Moulton. 

John F. Allen invents a valve-gear having a variable cut- 
off with positive movement, and introduces the multiport 
principle, and in 1863 makes it a balanced valve. 

Chas. T. Porter employs these inventions of Mr. Allen to 
make a high-speed engine with automatic cut-off. 

Charles T. Porter invents the isochronous spring-governor, 
using a spring with initial tension so as to exert a resist- 
ance which varies directly as the diameter of the circle 
described by the balls. This underlies the shaft-governor. 

Chas. B. Richards invents the first indicator in which the 
motion of the piston was multiplied. 

Hartnell of England patents control of throw of eccentric 



APPENDIX. 679 

by revolving weights balanced by springs, in plane ot ro- 
lation of the engine-shatt, bui moves eccentric trom ior- 
ward towards backward position, and not towards the 
centre of the shaft. 
1872-73. John C. Hoadley applies the balanced-spring shaft-governor 
to control the throw of a single piston-valve in an auto- 
matic cut-off engine by moving eccentric across the shaft 
and giving invariable lead but variable cut-off release 
and compression. 
1874. A. C. Kirk introduces triple-expansion in S.S. Propontis, 



NOTES. 

I. The sun's energy stored in vegetation in geologic times reappears in 
the burning of fuel. The sun also nourishes the plants which support 
animal life. Without the dynamogenous properties of sunlight ihere 
would be no motor forces. 

Potential energy becomes actual energy when it is allowed to produce 
motion, 

2-4. The science of Thermodynamics treats of the mutual convertibil- 
ity of heat and work, the indestructibility of force, and the conservation 
of energy. It belongs to the field of dynamic engineering. 

6. Since Mariotte's law gives /"ofo = /"z^, and its combination with Gay- 

Lussac's law gives ^-^-^ =^ , whence pv — RT, it follows that the sup- 

ply of heat and the supply of power to the engine are convertible terms. 
Hence a medium for conveying heat into the cylinder is valuable in pro- 
portion to its ability as a heat-carrier. Any other fluid can be used instead 
of water — air, alcohol, ammonia, bisulphide of carbon, etc., — but ihey re- 
quire a larger cylinder for equal power, or are troublesome on account ot 
leakage, or the difficulty of condensation or their cost. Gas-engines carry 
the heat into the cylinder directly. Consult Transactions A. S. iM. E., 
vol. X. p. 657. 

8. If the mean pressure and piston-speed in any district or at any period 
conform to accepted figures, handy approximate formulae for H.P, can be 
derived from the exact equation. The values for P average between 30' 
and 40 and for LN between 700 and 500 in ordinary Corliss practice and 
many short-stroke high-speed engines, or PLN = 21000. Hence the rough 
rule may be made for such engines that the horse-power is one half the 
square of the cylinder diameter. This must be used with caution, as it is a 
nominal horse-power, and is true only for certain conditions, and may lead 
to error when applied outside of them. 

9-10. To prove the efficiency of a typical steam-engine mechanism: If 
the connecting-rod be assumed to be of infinite length, or replaced by a yoke 
like that in Fig. 4, we have the most unfavorable case. Let P denote the 



680 APPENDIX. 

pressure on the piston-area, and V its velocity at any point of its traverse. 
Let p denote the tangential effort on the crank-pin revolving in its circular 
path and v its velocity. These may be uniform or constant, but in any 
case the time may be taken short enough to have them considered constant 
without error. 

li now a circle be drawn representing the path of the crank, and at any 
point the pressure P be represented in direction and intensity by a line 
parallel to the axis of the cylinder acting at that point, it can be decom- 
posed into two components at right angles, one tangential and one normal. 
The tangential component will be the effort p at that point, and will be 
perpendicular to the radius. The normal component will coincide with the 
radius produced. If the tangential component p be projected on the pis- 
ton effort /*, there will be three similar right-angled triangles produced. 
From these it will appear that the tangential pressure on the pin will equal 
the piston-pressure into the sine of the crank-angle, becoming equal to it 
at 90° and 270°, and being zero at 0° and 180°. The velocities of crank-pin 
and piston will be to each other in such a relation that the pin-velocity will 
*)e a mean proportional between the piston-velocity and the projection of 
the pin-velocity on the direction of the piston-velocity. (Legendre, Bk. IV, 
Prop. XXII). Hence, from what has preceded, 

v\ V :: p :P, 
or Pv=pV 

lor an instant of time and for any point. Hence, at any point the work 
given to the piston equals that received by the crank, less the loss from 
friction of joints or moving parts. In other words, the crank mechanism 
is theoretically perfect. 

II. For marine-engine mechanisms used in old vessels of British navy, 
consult John Bourne, Treatise on the Screw Propeller, London 1867, pp. 
380, 386. 

17, For a steam-balanced vertical engine, see Durfee, Trans. A, S. M. E. , 
vol. IV, p. 368, Nc. 125. 

23. For design of a walking-beam, consult Whitham. Steam-engine 



Design, p. 350; Constructive Steam Engineering, p. 594. I 

31. For steam-turbines see Trans. A. S. M. E.. vol. x. p. 680: vol. \ 

XVIT. p. 81. 

35. It has been urged that the short exposure of steam and metal of 
the cylinder to each other at high rotative speeds would diminish the 
reaction and interchange of heat. The interchange seems so instantaneous 
that the effect of high speed is less than was supposed. Consult Denton, 
Tians. A. S. M. E., vol. x. p. 722; Barr, Ibid., vol. xvi. p. 446. 

39. Authorities on Cornish engine are Pole, Wicksteed. and Farey> in 
Britain; Clarence King, on American practice. 

49. The injection must condense the steam to water by absoibing the 
heat of vaporization or latent heat, and must then lower the temperature 
of the water to that belonging to the pressure in the condenser. The total 



APPENDIX. 68 1 

heat of the steam at any temperature t which corresponds to the pressure 
of the exhaust-steam is given by the formula (from Regnault) 

^= i092 + .305(^ - 32) 

in British thermal units. The latent heat of vaporization is approximately 
given by the formula (Rankine, from Regnault) 

L — 1092 — o.-]{t — 32) 

Hence the weight w of steam carries a quantity of heat in thermal units 
represented by 

where /' is the final temperature of the steam condensed to water, and the 
injection mixed with it. The weight of injection-water w' is raised from 
the cold-well temperature t to the common final temperature t' \ these must 
€qual each other; or 

w' {t' - t)= w{Q- t') 

, w{ Q-i') 
whence w = — --, — 

As an example, if the steam came into the condenser at 35 pounds pressure 
above vacuum, with a temperature of 229° Fahr., it will carry 1152 units of 
heat per pound with it. If the final temperature of the condensed steam 
and injection is 120° Fahr. and the injection enters at Co", the weight of 
injection required will be 

, 1152 — 120 , . , . , , 

w = ^ = 17 -f times the weight of steam. 

The usual proportion is from 25 to 30 times in cool climates or seasons, 
with provision for 35 times in warm weather or climate. 

50. The Worthington self-cooling condenser is describeu by Mr. Louis 
R. Alberger, Trans. A. S. M. E., vol. xvii. p. 625, "A Self-cooling Con- 
denser." 

Other forms are designed by Mr. Geo. A. Barnard, using wire-gauze 
instead of tiles. See also Fitt, Evaporative Condenser Trans. A, S. M. E., 
vol. XIV. p. 690, No. 534 ; also Henrich. Trans. A. J. M. E. . 1895. 

52. For a surface condenser the same formula applies, but the injection 
is heated less, and so more weight is required, Whitham, A. S. M. E., vol, 
IX. page 427, gives 

^ = 7^-37 • 

in which 7 is the temperature of the steam at the pressure indicated by the 
vacuum-gauge, and Z's is the temperature in the hot-well. This latter is not 
the same as ti. as in the case of the jet condenser. This makes the ratio of 
circulating water to steam condensed approach 70, and gives a circulating- 



682 APPENDIX, 

pump from 1/20 to 1/30 of the cylinder volume, if single-acting. The sur- 
face for condensation is often made 2/3 of the boiler heating-surface. 

Seaton gives (Manual of Marine Engineering, p. 198) with the injection 
at 60° the following table : 

Absolute Term inal Pressure "^ den^i no'^n H.V^^ S"" 

6 1.50 

8 1.60 

10 1.80 

12.5 2.00 

15 2.25 

20 2. 50 

30 3.00 

Whitham's Rule (Trans. A. S. M. E. vol. ix. p. 425) is 

WL 



S=^ 



i8o(r, - 1)* 



in which / is the arithmetical mean temperature of the circulating water. 

The velocity of flow of water in condenser-tubes should be not less than 
400 nor more than 700 feet per minute. 

Experiments on condenser surfaces are by J. P. Joule, Jour. Franklin 
Inst., 1862, p. 36 ; by Isherwood, Shock's Steam-boilers, p. 58 ; by Nichol, 
Engineering of London, vol. xx., 1875, P- 449- 

53. The form of surface condenser shown is the design of Mr. Fredk. 
Meriam Wheeler. 

57. For description of Morton Condenser, see Jour. Frank, Inst., Nov, 
1868. Also Trans Inst, of Engineers of Scotland, 1868. 

63, See Robinson, Trans. A. S. M. E., vol. iii. p. 130, No. 64, 

65. See also Kent's Mech. Engineer's Pocket-book. p. 761 ; also D. K. 
Clark, Steam-engine. 

70. See Hoadley, Trans. A. S. M. E.. vol. i. p. 155, No. 12 ; also Trials 
of Steam Machinery of Revenue Steamers Rush, Dexter, Dallas. U. S. 
Treasury Dept.. Nov. 1874, by Messrs. Loring and Emery; also Tests ol 
U. S. Coast Survey Steamer Bache, May 1874, by Emery. Trans. A. S. C, 
E., Dec. 1874 ; also Tests of Gallatin, by Loring and Emery. 

72. Consult Whitham, Cylinder Ratios of Triple-expansion Engines, 
Trans. A. S. M. E., vol. x. p. 576. 

For Rockwood proportions, consult Trans. A. S. M. E.. vol. xiii. p. 647: 
vol. XVI. pp. 169, 179. 

75-78. The area of the diagram of effort (Figs, in and 112) can also be 
reduced by increasing the compression by early closure oi the exhaust- 
valve. The first effect is to cause the cylinder to pump pressure back into 
the boiler and convert work back into heat, which is a storing ot excess of 
energy, and thereafter the area of the card is diminished by moving the 
bounding curve at the right hand towards rhe left in those figures. Con- 



APPENDIX. 



683 



suit Tabor, Trans. A. S. M. E., vol. v. p. 48, No. 132. Thurston, Trans. 
A. S. M. E.. vol. II. p. 338, No. 45. 

76. Consult Porter, Trans. A. S. M. E., voL xvi. p. iii, No. 615. 

77. W. J. M. Rankine and Brownlee describe cylinder condensation and 
re-evaporation in Trans. Inst, of Engineers of Scotland, 1860-61. C. E. 
Emery describes experiments of 1864-68 with non-conducting linings for 
cylinders, Trans. A. S. M. E., vol. vii. p. 375, No. 204. See also vol. i. p. 
185. 

81. By reference to Fig. 131 it will be apparent that if the angular 
velocity of the crank-pin be oa^ the space described by it will be Rco, and 
the velocity of a horizontal piston will be Roo cos go. If the area of the 
piston be A, the volume to be filled in a time dt will be 



APgocos go dt. 



(i> 



If X denote the linear velocity of flow of steam through the port in the 
valve-seat whose length is /, and r be the radius of the valve-crank, then 
during the same time dt the motion from its central position for the same 
angular velocity go will be rcos Godt, opening" an area /r cos go dt through 
which a volume of steam passes equal to 



xlr cos GO dt. 



(2> 



Since these should be equal to each other, by equating (i) and (2) the 
value of X becomes 



AR, - 



(3> 



which is a quantity involving the crank-pin or rotative speed only, which 
is common to both cranks, and the arbitrary constants which fix the linear 
velocity of the steam. In other words, the steam enters at all angles with 
the velocity determined by cylinder volume and port-area, and not by- 
variation in relation of the crank angles. 

93. Consult also Catechism of the Locomotive Engine, by M. N. Forney. 
Also, D. K. Clark, Railway Machinery (very full discussion). 

94. Prof. Zeuner's demonstration seeks to find the distance the valve 
has moved from its central position when the main crank and valve-crank 




have moved through an angle 00. If r is the radius of the valve-crank, / 
and h the lengths of the valve-rod to the knuckle-joint and the valve-stem. 



684 APPENDIX. 

proper respectively, then from the diagram in which the line through X 
iixes the central position of the valve, the length BX may represent the 
space the valve has gone to the right for the angles 5 and cd. If this 
distance be called |, then 

^ = BX=OB - OX. 

To find a value for OB: 

0B= 0E-\- EBx + BBx 



= 0E^ BBi + VDB,'' - DE'^ 



= r sin (£»+5)-f /, -\-^ P - r' cos^ (a? + 5). 

But (/ - tli2?!^+iy = I. _ .. cos' (0. + a) + tl££!l^ 
.-. 05 = . sin (^ + 5) + A + / - il£2!!i?jt«). 

when the last term is neglected as being so small a quantity as to be nag- 
ligible. 

Similarly, a value for OX\s 



2 ,2/ 

Combining these values and substituting, 
^^= ^ = ^ Sin (oj -I- 5) +/i + / ^- — ■ — '-— h +/ — 

= r sin (a? + 5) + -^ cos^ 8 - cos' (<» + 5) | 

= r sin d cos CO -f- ^ cos 5 sin go -\- E. 
If r sin 6 = A 

and r cos d = B, 

^ = A cos ft? -f- ^ sin tt) -j- i?; 

^is a term to include the motion due to the angularity of the valve-rod. 
It is a small quantity, because the length / is always great compared to r, 
and the cosines of the angles are small, and their squares smaller. The 
quantity E may therefore be dropped for convenience, or treated as a 
" missing quantity." 

The equation for ^ will give also the value of the radius vector if a pole 
be taken in the circumference of a circle the co-ordinates of whose centre 



APPENDIX. 



685 



are O^ = fl = - 
2 



and BC = b — —, and whose diameter is r, 
2 



For if Pi be 



any point whose radius vector is OPi and the angle MOP = go, then if 

OM— k cos 00, 
and 

MP = ^ sin w 
it can be proved that 

CN'' 4- NP'' = cp'' = r ) , 

(?cos(»-a)2 j-(^sinaj-^)2 = f-J , 
2 cos' a? — 2a ^ cos a? + «' 



+ ^' 



^* (cos2 ft> + sin' go) 

-\- b sin go), 
whence 

I = 2a cos ft? -f 

and if 



2<5|sin(» + ^'= [-] , 
2{a cos ft? 



2^ sin ft?; 




Fig. 510. 



2a = ^ and 2.b = B, 
^ = A cos ft? + ^ sin ft?. 
Or in other words, the motion of the valve from its central position may be 
represented by, or replaced by, the length of the radius vector of a polar 
circle, whose diameter is the throw of the valve. The radius vector when 
ft? is zero determines the angle P3OP, because the main crank being at its 
dead-centre the valve should have a radius vector equal to the sum of the 
lap and the lead. 

96. The authorities on valve-gears are : 

E. J. C. Welch : Designing Valve-gears. 
H. W. Spangler : 

C. H. Peabody: 

F. A. Halsey : 
Hugo Bilgram : 

Holmes on the Steam-engine. 
Blaha, Schiebersteuerung. 
103. Consult Robinson, Trans. A. S. M. E., vol. iv. p. 150, No. 97 
103. To evaluate the pressures to be balanced on a slide-valve, suppose 
a locomotive-valve 17 inches wide and io| inches long, having a lap of i 
inch a travel of 4 inches, a port of 14^ by i} inches, and an exhaust hol- 
low of 6 X 14^ inches. Let the valve be working with the lever in the eight- 
inch notch, or cutting off at one third stroke. The following areas and 
pressures will prevail : 

Port-area = 18 square inches (^) 

Exhaust-hollow =87 square inches (2) 

Gauge-pressure = 160 lbs. per sq. inch .... (3) 



686 APPENDIX. 

Back-pressure = 5 lbs. per sq. inch ... (4) 

Mean pressure = no " " '« " ... (5) 
Cushion-pressure = 40 " •» «< ♦♦ , , , (6) 

The downward pressure during admission, or one-third stroke, is ex- 
erted on 10 X 17 — 170 square inches. 

After cut-off, during expansion, or two-third stroke, the whole area 
receives pressure = io| X 17 = 178 square inches. The average area or 
174 square inches receives a downward pressure of 160 lbs. per square 
inch = 27S40 lbs., or nearly 14 tons. 

Upward pressure from the cylinder relieves this somewhat. 

In the one third during admission (2) has (4) upon it = 435 lbs. 
" " second third, (i) has (5) upon it = 1980 " 

" '• " " (2) •• (4) " " = 435 " 

" " third third (i) " (6) " " = 720 " 

" «« - - (I) - (5) .' '« = 1980 " 

Summation = 5550 lbs. 
or an average through the stroke of 1850 " 

Subtracting this from the average downward pressure 27840 — 1850 = 25990 
lbs. net average downward pressure. 

no. Consult Uhland-Tolhausen, Corliss Engines, London, 1879. Also 
J. T. Henthorn, on the Corliss Engine. 

112. A disadvantage of the trip-gears is the variable length of the valve- 
travel, whereby the valve-seat is worn unequally. 

114. For authorities on link-motion consult : 
Rankine, Machinery and Millwork. 
Zeuner, Treatise on Valve-gears. 
W. S. Auchincloss, Link and Valve-motions. 
N. P. Burgh, Link-motion and Expansion-gear, London, 1870. 

125. For a locomotive steam reverse-gear with hydraulic stop-cylinder, 
consult R. R. Gazette, Nov. 18, 1881. Also Recent Locomotives, 1886, Figs. 
29-31. 

131. Consult Weisbach-Herrmann-Klein, Mechanics of Engineering, 
vol. III. Part I. Section II. p. 990, Edition of 1890. 

140. For shaft-governors, see Thurston, Manual of the Steam-engine, 
Part II. p. 292. Also, Trans. A. S. M. E., vol. xi. p. 1068, 1081 ; vol. 
XIV. p. 92 ; XV. p, 929 ; vol. xvi. p. 729. 

147. For Svedberg's marine governor operating by varying immersion 
of the stern of the vessel, consult Whitham, Const. Steam Engineering, p. 
372. 

152. Consult Whitham. Const. Steam Engineering, p. 129. 

159. The cylinder volume at a given speed of rotation should be a maxi- 
mum to make PV a. maximum (parag. 6); but to diminish the surface of 
metal radiating heat outwardly and absorbing it from the steam, such sur- 
face should be a minimum. Such minimum surface is when the stroke 
equals the diameter, and were all surfaces of equal effect this would give 
best results.' (For calculation of minimum, see Thurston. Manual of the 
Steam-engine, Part II. p. 65,) But the heads and the piston are much 



APPENDIX, 687 

more effective areas for condensation in an expansive engin-e than the bar- 
rel or cylindrical part; hence the diameter had better be reduced relatively 
to the length of the stroke. Hence a long-stroke engine results, with a 
stroke twice the diameter or even greater. Clearance losses are less in a 
long cylinder also. 

162. For steam-jacket, see Loring and Emery, note 70 ; also Tests of 
U. S. S. Gallatin, Dec. 1874 and Jan. 1875 ; also Paper on Cylinder Con- 
densation and Superheating, Soc. of Arts, Mass. Inst. Tech., April 1875, 
by Geo. B. Dixwell ; also Thurston, Trans. A. S. M. E., vol. xv. p. 779, 
No. 590, and vol. xvii. p. 488, No. 689. 

For Superheating, see Isherwood, Experimental Researches, vol. 11.; 
Experiments on U. S. S. Mackinaw, Eutaw, and Georgeanna. 

164. Consult Robinson, Trans. A. S. M. E., vol. 11. p. 19, No. 20; also 
Rutherford-Hutton, Trans. A. S. M. E., vol. viii. p. 439, No. 246. 

170. Consult Emery, Trans. A. S. M. E., vol. 11. p. 40, No. 22. 

172. For Parallel Motions, see Arthur Rigg, Treatise on the Steam En- 
gine, 1878, p. 130. Also Weisbach-Herrmann-Klein, Mechanics of Engi- 
neering, vol. III. Part I. Section I. p. 425. Also Rankine, Machinery and 
Millwork, p. 274. 

173. For effect of connecting-rod upon the crank-pin effort, see Arthur 
Rigg, Treatise on Steam Engine, 1878, p. 258. 

174. A rectangular or flat tapering key is often called a cotter. Hence 
what is here called the gib and key is ofted called the gib and cotter. 

184. Accepted fly-wheel formulae for the weight of rim are : 

A St) 
\i) W = 2So,ooo —^^, (Thurston) 

or 

AS 
{2) ^= 12,000,000— — 2 (Thurston) 

in which A = piston-area in square inches, 5 is the stroke in feet, /> is the 
mean pressure of steam in pounds per square inch, R is the revolutions per 
minute, and D the outside diameter of the wheel in feet 

cx n H P 1 

(3) W= — ^3' ,' '-* (Rites, A. S. M. E., vol. xiv. p. 100) 

In this C varies from ten billion to twenty billion for single-acting 
Westinghouse engines for electric lighting. For ordinary double-acting 
engines use five billion. 

(4) ;^= 700,000 ^^-^2- (Stanwood) 

In this 5 is the stroke in inches, and 8 the diameter of cylinder in 
inches, and the factor 700,000 is to be used when the piston-speed will not 
fall below 480 feet per minute, and electric-lighting standard of regularity 
is exacted. For ordinary duty slide-valve engines, use 350,000 ; for Corliss 
engines for electric lighting, use one million. 

<5) ^= 387-587.500 ^^^i^E^^l^ (Whitham) 



688 



APPENDIX. 



Here A' is a permitted ratio of excess or deficiency of crank-effort to the 
whole crank-effort, and \/n is a fraction denoting the variation of speed — 
say i/io from to i/ioo. 

Consult : Thurston, Manual of the Steam-engine, Part II. p. 415. 
" Whitham, Steam-engine Design, p. 199. 

** Kent, Mechanical Engineer's Pocket-book, p. 817. 

187, Consult: Stanwood, Trans. A. S. M. E., vol. xiv. p. 251. 
" " " " vol. XV. 

" Lanza, " " vol. xvi. 

" Manning, " " vol. xiii. p. 618. 

" Kent, Mechanical Engineer's Pocket-book, p. 820. 
191. The area of the pipe in square inches should be 

_ Area of cylinder in inches X piston-speed 

Area — ^ _ -r ; ; ; ; 

Mean velocity of steam in pipe in feet. 

The numerator in the second member is a volume V, If it be mul- 
tiplied by an assumed mean pressure {P) in the cylinder — perhaps 40 — and 
divided by 33,000, and a velocity of 6000 feet per minute be taken for the 
steam, the formula becomes a formula for area in terms of horse-power; 
and' with these values 

Area = .1375 H.P. 

Another form of the pipe formula is 

/hTr 



H.P. = 6^2 or pipe diameter = |/ — '-—^ = 0.408 4/H.P. 

Exhaust-pipes should compel a steam velocity of 4000 or 5000 feet per 
minute only. 

For steel-riveted pipe, see Manning, Trans. A. S. M. E., vol. xv. p. 57i^ 
195, Authorities on non-conducting coverings: 
Emery, Trans. A. S. M. E., vol. 11. p. 34. 
Hutton, " " vol. III. p. 228. 

Ordway, " " vol. v. pp. 73 and 212. 

" " vol. VI. p. 168. 

Brill, " " vol. XVI. p. 827. 

197. Consult Trans. A. S. M. E., vol. xvii. p. 295, No. 678. 
204-206. Consult Kent's Mechanical Engineer's Pocket-book, p. 700. 
207. Let an element of the arc of the semicircle be denoted by c/x 
measured along the tangent, and suppose its length perpendicular to the 
paper to be one inch. Then the area of that element will be i X «'-^ and the 
normal pressure on it Pdx. If this normal be decomposed into horizontal 
and vertical components, only that perpendicular to AB tends to rupture 
the joints at A and B. The horizontal components tend to produce rupture 
along EP. Hence the component V which is Pdx cos a produces the same 
effect as the force P acting over the area 7 X ^c, since 6c = dx cos a. There- 
fore the total upward force is the sum of the projections of all elements of 
the semi-cylindrical arc, or is equal to PD. Or, again, Pdx cos a may be 
integrated between « = -|- 90 and a = — 90, which becomes P(/^ -{- P) = PD. 
The sketch at the right shows the reasoning when a solid mass like wood 



APPENDIX. 



689 



transmits the pressure to the arc just as the fluid does, and shows the rup- 
turing force to be proportional to the diameter. This was first proposed 
Dy Forney. 





Fig. 512. 



213. For punched and drilled plate tests, see Engineering of London, 
June 1879. 

215. For hand and machine riveting compared, and strength of machine- 
riveted joints, see Tests of Greig and Eyth, reported in Engineering of 
London, 1879. 

216. The Hartford Steam-boiler Insurance Co. have published the fol- 
lowing table for iron plates and iron rivets : 

TABLE OF PROPORTIONS FOR RIVETED JOINTS. 



Thickness of plate 

Diameter of rivet 

Diameter of rivet-hole. . 
Pitch, single-riveting.. 
Pitch, double-riveting. . 
Efficiency, single-riveting 
Efficiency, double-riveting 

For steel plates and iron rivets they advise the use of the following 

TABLE OF PROPORTIONS FOR RIVETED JOINTS IN STEEL 
PLATES WITH IRON RIVETS. 



1/4 in. 


5/16 in. 


3/8 in. 


7/16 in. 


1/2 in. 


5/8 in. 


ii/i6in. 


3/4 in. 


13/16 in. 


7/8 in. 


11/16 in. 


3/4 in. 


13/16 in. 


7/8 in. 


i5/i6in. 


2 


2tV in- 


2| in. 


2t\ in. 


i\ m. 


3 


3iin. 


3iin. 


3|in. 


3|in. 


.66 


.64 


.62 


.60 


.58 


.77 


.76 


.75 


.74 


-73 



Thickness of plate 


. 1/4 in. 


5/16 in. 


3/8 in. 


7/16 in. 


1/2 in. 


Diameter of rivet 


. Ii/i6in. 


3/4 in. 


13/16 in. 


7/8 in. 


15/16 in. 


Diameter of rivet-hole. . . 


• 3/4 in. 


i3/i6in. 


7/8 in. 


15/16 in. 


I in. 


Pitch, single-riveting . . . 


2 in. 


2tb in. 


2I in. 


2^in. 


2\ in. 


Pitch, double-riveting. . . 


3 in. 


3|in. 


3^ in. 


3|in. 


^\ in. 



From the above it appears that the only change from the former table 
consists in making the rivets just 1/16 of an inch larger for each thickness 
of plate. This, on the assumption that the best rivets resist a shearing- 
stress of 48,000 lbs. per square inch of section, will give about equal 
strength to plate and rivet. 

The following are the latest instructions issued by the British Admiralty 



690 APPENDIX. 

for testing steel rivets. The rivets are to be made from steel bars, having- 
an ultimate tensile strength of not less than 58,000 pounds per square inch of 
section nor more than 67.000 pounds, with a minimum elongation of not 
less ihan 20 per cent in a length of 8 inches. A portion of one bar in 
every fifty to be taken for iesimg before being made into rivets. Pieces 
cut from every bar, heated uniformly to a low cherry-red, and cooled in 
water at 82° F., must stand bending in a press to a curve of which the 
inner radius is equal to the radius of the bar tested. Rivets are to be 
properly heated in making, and the finished rivets allowed to cool gradually. 
The rivets are to stand the following forge tests: (i) The shank to be 
bent double cold, without fracture, to a radius equal to the radius of the 
shank. (2) Bent double hot, without breaking, to as small a radius as 
possible. (3) Flattening of the rivet-head while hot. without cracking at 
the edges — the head to be flattened until its diameter is 2\ times the 
diameter of the rivet-shank. (4) The shank of the rivet to be nicked on 
one side, and bent over to show the quality of the material. One rivet in 
every hundred to be forge-tested as a sample. 

Consult also Kents Mechanical Engineer's Po',\''t-book, p. 354. 

232. The U, S. Federal laws fix the formulae which are to be used in 
proportioning flues against collapse. They may be grouped as follows : 

Case A, For lap-welded flues greater than 7" in diameter and less than 
16", and 18' long or less; 

For each 3' of length add y^o °^ ^'^ inch to t. One wrought-iron stiffening- 
ring to be used in each 5', whose f =t, and whose width is greater than 

■^¥ • 

Case B. Flue greater than i6" diameter and less than 40": 

C 
Case C. Flues greater than 40": 

P = FRankine uses 80600] 

Case D. Corrugated flues, j-\" thick or thicker, and the corrugations 
I^" deep, 6" pitch: 

_ 14000 X T 

In these formulae 

D ' 

7'= thickness in inches; 

/* = allowable pressure in lbs. per square inch; 
C = constant 0.31 ; 
D — diameter in inches; 
L = length in feet (not over 8')- 
These were supplemented in January 1894 by adding : 



i 



APPENDIX. 



691 



THICKNESS OF MATERIAL REQUIRED FOR TUBES AND FLUES NOT OTHERWISE 

PROVIDED FOR. 

' 9. Tubes and flues not exceeding 6 inches in diameter, and made of 
any required length ; and lap-welded flues required to carry a working steam- 
pressure not to exceed 60 lbs. per square inch and having a diameter not 
exceeding 16 inches, and a length not exceeding 18 feet ; and lap-welded 
flues required to c^irry a steam-pressure exceeding 60 lbs. per square inch, 
and not exceeding 120 lbs. per square inch, and having a diameter not ex- 
ceeding 16 inches and a length not exceeding 18 feet, and made in sec- 
tions not exceeding 5 feet in length, and fitted properly one into the other, 
and substantially riveted; and all such tubes and flues shall have a thick- 
ness of material according to their respective diameters, as prescribed in 
the following table : 



Outside 
Diam. 


Thickness. 


Outside 
Diam, 


Thickness. 


tside 
Diam. 


Thickness. 


Outside 
Diam. 


Thickness. 


I in. 


.072 in. 


2| in. 


.109 in. 


5 in. 


.148 in. 


12 in. 


.229 in. 


I^ 


.072 


3 


.109 


6 


.165 


13 


.238 


'i 


.083 


3i 


.120 


7 


.165 


14 


.248 


If 


.095 


3- 


.120 


8 


.165 


15 


.259 


2 


.095 


3| 


.120 


9 


.180 


16 


.270 


2i 


.095 


4 


.134 


10 


,203 






2^ 


.109 


4| 


.134 


II 


.220 







" 10. Lap welded flues not exceeding 6 inches in diameter may be made 
of any required length without being made in sections. And all such lap- 
welded flues and riveted flues not exceeding 6 inches in diameter may be 
.allowed a working steam-pressure not to exceed 225 pounds per square 
inch, if deemed safe by the inspectors. 

" II. Lap-welded flues exceeding 6 inches in diameter and not exceed- 
ing 16 inches in diameter, and not exceeding 18 feet in length, and required 
to carry a steam-pressure not exceeding 60 pounds per square inch, shall 
not be required to be made in sections. 

" 12. Lap-welded and riveted flues exceeding 6 inches in diameter and 
not exceeding 16 inches in diameter, and not exceeding 18 feet in length, 
' and required to carry a steam-pressure exceeding 60 pounds per square 
inch and not exceeding 120 pounds per square inch, may be allowed, if 
made in sections not exceeding 5 feet in length, and properly fitted one into 
the other, and substantially riveted. 

" 13. Riveted and lap-welded flues exceeding 6 inches in diameter and 
not exceeding 40 inches in diameter, required to carry a working steam- 
pressure per square inch exceeding the maximum steam-pressure prescribed 
for any such flue in the table of section 8 of this rule, shall be constructed 
under the provisions of section 15 of this rule, and limited to the working 
steam-pressure therein provided for furnace-flues; but in no case shall the 
material in any such riveted or lap-welded flue be of less thickness for any 
given diameter than the least thickness pres«ribed, in the aforementioned 
table, for flues of such diameter." 



692 APPENDIX, 

236. See Whitham, Effect of Retarders. Trans. A. S. M. E., vol. xvii, 
p. 450, No. 687. 

237. For the holding-power of tubes expanded into tube-sheets see 
experiments by C B. Richards at Colt's Patent Fire-arms Co. for Hartford 
Steam-boiler Ins. Co., published in The Locomotive for June 1881. 

253-4. Consult Shock. W. N., Steam Boilers, 1880. 

273. See Whitham, Autom. Mech. Stokers, Trans. A. S. M. E., vol.. 
XVII. p. 558, No. 690. 

283. Other chimney formulae are: 

For iron stacks. A' = .0008^ 



Ti 



yHiTr - Tay 
Ti 



For brick Stacks, A' = .ooitF 3 



\/II{T,- TaY 

in which Ti is the temperature at the bottom of the stack, Ta the temper- 
ature of the air, i^ the height in feet above the grate. The constant is a. 
factor for friction. Twenty-two pounds of air go for each pound of fueh 
(Gale, Trans. A. S. M. E., vol. xi. p. 451.) 
Consult also: 

Peclet, Traiti de la Chaleur, in the 3d ed. i860, p. 217, § 491. 
Wood, Trans. A. S. M. E., vol. xi. p. 974. 
Webb, " " " XI. p. 762. 

" " " '* XI. p. 772. 

Wood, " " " XI. p. 984. 

Thurston, " " " xii. p. 85. 

For interference of flue-currents, taking into a common chimney, consult 
Peclet, Traiti de la Chaleur, in the 3d edition, i860, vol. i. p. 206, § 474. 

285. Consult Peclet, Traits de la Chaleur, in the 3d ed. i860, p. 252, 
§571, vol. I. 

For the steam-jet consult Ibid., chap. vii. p. 279, § 619. See Forced 
Combustion in Steam-boilers, by James Howden, section of Naval Engin- 
eering, Congress of Engineering at Chicago, 1893 ; also Roney, Trans. 
A. S. M. E., vol. XV. p. 1162 ; also, Kent, Mechanical Engineer's Pocket- 
book, p. 714. 

287. Coal-calorimeters may be studied by reference to : 

Barrus, A Coal-calorimeter, Trans. A. S. M. E., vol. xiv. p. 816. 
Mahler's Tests of Coals, Mineral Industry, vol. i. p. 97. 
Carpenter's Coal-calorimeter, vol. xvi. Trans. A. S. M. E., p. 1040. 

Dulong's formula for the heating-power of a coal, in British thermal 
units, is 

Calorific power = 14500 C -f 62500 (H — 0/8), 

in which C, H, and O are the percentage of carbon, hydrogen, and oxygen 
divided by 100 to reduce them to unity. 

See also Kent, Mechanical Engineer's Pocket-book, p. 633, and Emery^ 
Trans. A. S. M. E., vol. xvii. No. 677. 

290. Heat and Heat-engines, by W. P. Trowbridge, 1874, page 153. 



APPENDIX. 693 

291. The steam-tables most used are those by — 

Zeuner, Warmetheorie. 

Porter, C. T, The Steam-engine Indicator. 

Trowbridge, Heat and Heat-engines. 

Peabody, C. H., Steam-tables. 

Rontgen, Rob't, tr. by Du Bois. Principles of Thermodynamics. 

292. C. E. Emery, Report of Judges of Group XX, International Ex- 
hibition of 1876, p. 131. J. B. Lippincott & Co., Phila., Pa. See also 
Estimates for Steam Users, Emery, Trans. A. S. M. E., vol. v. p. 284, and 
Cost of Steam Power Produced with Engines of Different Types, Emery, 
Trans. Am. Inst. Elect. Eng'rs, March 1893 (from which the table is taken). 

296. The formula for heat of combustion is 

rp 1 , .^ f f 1 i (^1 — ^2) X weight of gas and air X sp. 

Total calorific power of fuel= ] ^^^^ ^^ products of combustion. ^ 

If the total heat of carbon burned to CO2 be 14,500 heat-units and 24 
pounds of air is used and one pound of carbon, and if the mean specific 
heat be called 0.237, then 

7',-7', = -H52^ = 2447Fahr. 
25 X. 237 

The minimum pounds of air per pound of analyzed fuel are given by the 
formula 



Air = 12C + 36 



("-?)■ 



Consult C. Wye Williams, Combustion of Coal, 1854. 
298. Consult Hodgetts, Liquid Fuel. 

300. For data and tables, see " Helios," by the Heine Steam-boiler Co. 
of St. Louis, 4th ed., 1895, p. 36. Also Colliery Engineer, 1889-90, for 
articles by F. ]. Rowan. Also D. K. Clark, Treatise on Steam engine. 

301. See Reports on Smoke Prevention, Journal of Assoc. Engineering 
Societies, vol. xi, June 1892, p. 291. See also /r^« Age, April 7, 1892. Also 
O. H. Landreth, Report to State Board of Health, of Tennessee. See also 
Eng'g News, June 8, 1893; also Report, March 10, 1888, by C. E. Jones and C. 
F. White to O. N. Nelson, City Council of Chicago. See also C. Wye Will- 
iams, Combustion of Coal' and Prevention of Smoke, London, 1854. See 
also D. K. Clark, Treatise on the Steam-engine; see Bryan, Down-draft 
Furnace, Trans. A. S. M. E., vol. xvi. p. 773. 

303. The specific gravity of mercury is 13.596. If 30 inches of mercury 
balances one atmosphere of 14.7 pounds pressure per unit of area, one inch 
corresponds to 0.49 lb. or one pound to 2.04 inches of mercury of that 
gravity. Impurity in the mercury changing its specific gravity changes 
the reading. 

Consult, for mercury columns. Trans. A. S. M. E., Melvin, vol. 11. p. 98; 
also, vol. XI. p. 892. 

317. For the thermodynamics of the injector, consult; 
Peabody, C. H., Thermodynamics, Chapter X, p. 145. 
Wood, De v., " page 279. 

Rontgen, Robt.. " Chapter XXII, p. 531 (Du Bois' trans.). 



694 APPENDIX. 

Theory and Practice of the Injector, Strickland L. Kneass. 
Kent, Mechan. Engineer's Pocket-book, p. 725. 

Consult also Trans. A. S. M. E., vol. x, Webb, pp. 339, 888. 

320. If the 

[total heat heat of steam — heat of cold feed] = x, 
and the 

[total heat of steam — heat of hot feed] =_y, 

then X — y gives the units of heat per pound of feed-water saved by pre- 
heating by waste heat. Then the saving in percentage will be 



X 

when expressed decimally 

321. For composition of fusible alloys, consult Kent's Hand-book for 
Mechanical Engineers, p. 333. 

Newton's alloy is 50 Bi + 31.25 Pb + 18.75 Sn, and melts at 212° Fahr. 
Others are 50 Bi + 10 Pb+40 Sn, " " " 240° " 

50 Bi + 50 Sn " " " 286° " 

66Pb4-33 Sn " " " 360° " 

324. The loss from blowing hot water from a boiler is found by thc- 
following : 

Weight evaporated (total heat — feed heat) = x 

Weight blown out (sensible heat — feed heat) —y 

Total =: X -\- y 
= loss in per cent by blowing down. 

325. For safety-valve formulae, consult Rankine. Steam-engine, p. 553; 
Kent, Mechanical Engineer's Pocket-book, p. 721. Experiments on Flow of 
Steam, by R. D. Napier (see Engineer of London, Sept. to Dec. 1869), gave 
for discharge from a conoidal nozzle per inch of area per second, provided 
the pressure into which steam f^ows is less than three fifths of that in the 
boiler from which it flows, 

/'. 
70* 
or, for an area of a square inches, 

pia , 70«/ 

aw = - — , whence fl = , 

70 p, 

in which w should be the entire weight of water which the heating-surface 
can evaporate in one second of time. Some other formulae for safety-valve 
areas are: 

rgra,e.ajea-l ^ T^ate of combustion inl ^ [P-nds of wateH 
^ ^ |_ m sq. ft. J ^ |_ po unds per sq. ft. J ^ [pf c^al per hou J 

36oOiP 

coal burned per hour , • i. . l^, x 

= ^ (assuming that 10 lbs. of water are evaporate^ 

5.14^ 
per pound of coal) ; or 



APPENDIX. > 695 



or A — \ sq. in. to 25 sq. ft. H. S.; 

or ,/i = I sq. in. to i sq. ft. G. S. 

The lift of a safety-valve is usually a very small quantity. The standard 
experiments on a conical seated valve four inches in diameter are those of 
Burg in Vienna. His values were, with a pressure below the valve of 

12 20 35 45 50 70 90 
the lift of the valve in inches was 3^ A 51 eV sV t^^ ik 
The area of the opening is the cylinder or cone included between the 
valve and its seat when the valve is open. Its area will be the circum- 
ference of the valve, multiplied by the foregoing small lift. 
326. The equation for a safety-valve of lever type is 

(/'X^)X l = WL, 

in which A is the area is square inches; P the pressure on each square 
inch; ^ the weight in pounds on the long arm of the lever, and strictly 
should cover the weight of the lever-arm, applied at its centre of gravity; 
L is the length in feet or inches from the fulcrum to the weight; and / is 
the length in the same unit from the fulcrum to where the spindle of the 
valve presses up against the lever. The U. S. law compels / to be more 
than 4 inches, and L cannot be over 40 inches. 

332. The table on page 696, compiled from various sources by Profs. 
Peabody and Miller, is reproduced by permission. 

353. If 10 square feet of plate one quarter of an inch thick be overheated 
so as to be at 1000° Fahr., it will represent 100 lbs. weight of iron, with a 
specific heat of 0.112. If water come on that plate at a temperature of 
even 300° Fahr., it will cool the plate by a transfer of heat to the water; 
whence 

^ = 7^ X ^'X (/"i - ^) — loox 0.112 X 700 = 7900 

units of heat received by the unknown weight of water. It takes about 
1000 units of heat to vaporize a pound of water under the pressure corre- 
sponding to 300° Fahr., or that plate would vaporize about 7.9 lbs. of water 
only, or less than a gallon, in being cooled to the temperature of the rest 
of the boiler. The volume of one pound of steam at 300° is 6.28 cubic feet, 
so that this steam would occupy but 7.9 X 6.28 or 49.6 cubic feet in the 
boiler. 

353. The following formula, due to Zeuner, shows the time to be allowed 
to a boiler to pass from one pressure or temperature to another. The 
lower pressure (/) may be that of the cold feed-water, in which Z" will give 
the time required to get up the steam-pressure corresponding to any higher 
temperature (/,)■: or t may correspond to the working-pressure, and /, be 
that corresponding to a pressure which will endanger the shell. 

Let 7"= time in minutes elapsing between the period when a lower 
temperature {t) prevails, and that at which (/,) will be the 
temperature when all outlets are closed for steam or dis- 
charge of heat ; 



696 



APPENDIX. 


















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APPENDIX. 6c^7 

t = temperature corresponding to the lower pressure ; 
/i = " '* " " higher pressure ; 

^= weight of water in the boiler ; 

^ = quantity of heat in B.T.U. transferred to the water in the 
boiler per minute. 

Then T= — — -. 

The quantity Q for any boiler is found from the expression 

(heating - s u r -\ /pounds of water\ /the quantity of 
face of boil- ] w / evaporated per \w/ heat absorbed 
er in square \ \ hour per sq. foot \ \ in evaporating 
feet / \ of heating-surface / \ i lb. of water. 



60 

The third factor in the numerator is 966 at atmospheric pressure. For 
higher pressures it may be called 1000, to make round figures. 
Illustrations of the application of this formula would be : 
Case i. Locomotive Boiler, 

W = 5000 lbs. of water ; 
Grate-surface = 11 sq. ft., and each square foot burning 60 lbs. of coal will 
evaporate 7 lbs. of water per pound of coal per hour, or 
77 lbs. of water per minute ; 
/ =r working-pressure of 90 lbs. = 319° Fahr. ; 
/i = dangerous " " 175 " =371° 



t, - t - 50° + Fahr. 

5000 X 50 

Hence T= = 3.2 minutes. 

77 X 1000 

Case 2. Marine Boiler, Flat Surfaces. 
IV ■=^ 79,000 lbs. of water ; 
Heating-surface = 5000 square feet, evaporating 3 lbs. of water per hour, 
or 250 lbs. per minute ; 
/ = working-pressure of 37 lbs. = 262° Fahr.; 
ti = dangerous " 60 '* = 291° '* 



ti — t= 29° " 

^ 79000 X 29 

T = — — ; = 9.1 minutes. 

250 -f 1000 

Case 3. Fire-engine {a) Boiler to get up Steam. 

^=93 lbs. of water, or about i\ cu. ft.; 
Heating-surface = 157 sq. ft., evaporating i lb. of water per hour, or 2.6 
per minute ; 
/ = atmospheric pressure, or 212'' Fahr. 
tx = working " of 329° or 100 lbs. pressure ; 



t,-t= 117° 

Then T= —■ —- = 4.2 minutes. 

2.6 X 1000 



698 



APPENDIX. 



Case 4. Same Boiler {bi) to become Dangerous. 
W — 338 lbs. of water ; 
ti = 200 lbs. pressure, or 388° Fahr. 
Then t^ — t^— 49°, 

and T = "^f ^ ^ '^^ = 6.4 minutes. 

2.6 X 1000 

It will be apparent that the danger increases with the heating-surface,, 
and diminishes with the greater weight of water contained in the boiler. 

354. Nystrom, p. 393, gives dynamic work of gunpowder at 150,000 to 
200,000 foot-pounds per pound of powder. Even at atmospheric pressure^ 
the energy resident in one cubic foot of water heated to form steam-gas at 
that pressure is 

1700 X 144 X 14-7 = 3.598,560 foot-pounds, 
which if all released at once as gunpowder gasefies would bear a ratio of 

destructive energy of , or nearly 18 times that of such powder. 

^•^ 200000 

368. For testing of power-plants, see Carpenter, R. C, Experimental 
Engineering ; Trans. A. S. M. E., Standard Methods for Testing Boilers, vol. 
VI. p. 256, No. 168 ; Standard Methods for Conducting Duty Trials of 
Pumping-engines, vol. xi. p. 654, vol. xil. p. 530, No. 381 ; Standard 
Methods for Testing Locomotives, vol. xiv. p. 1319, No. 552 ; Tests of a. 
Warm-blast Apparatus, Hoadley, vol. vi. p. 676. See also Peabody, Ther- 
modynamics, pages 338 to 394 ; Reports and Awards, Group XX, Inter- 
national Exhibition of 1876; Kent, Mechanical Engineer's Pocket-book, 
p. 685. For certain standard tests and methods for conducting them see 
Trans. A. S. M. E., Denton, vol. x. pp. 722, 792 ; vol. xi. pp. 328. 372 ; vol. 
XII. pp. 326, 975; vol. XIV. p. 1340; vol. XV. p. 882; vol. XVI. p. 913. 
Consult also Thurston, Handbook of Engine and Boiler Trials ; and Thurs- 
ton, Manual of the Steam-engine, Part II, pp. 583 to 722. 

370. Ball Pyrometer for Flue-gases. 

Since w X c X {t' — t) = w' X c' X {t" — /) in a transfer of heat, if a known 
weight of iron w, with a specific heat of 0.112 be cooled from an unknown 
temperature t' by immersing it in a tub of water containing a known weight 
of w' pounds at an initial temperature t" (both found by observation) and 
the water is raised by the ball at t' cooling to the final temperature t 
observed when the ball and water are at the same temperature, the only 
unknown is /', and can be calculated. The specific heat of water, c\ is unity. 

371. Coil calorimeter, see Trans. A. S. M. E., vol. vi. p. 296. 
Superheating calorimeter, see Trans. A. S. M. E., vol. vii. p. 178; vol. 

viii. p. 235. 

Throttling calorimeter, see Trans. A. S. M. E., vol. x. p. 327. 

Universal, or combined separating and throttling type, vol. xi. p. 790. 

For the errors, and for the necessary care in handling calorimeters, see 
Trans. A. S. M. E., vol. xi. p. 193; vol. xii. p. 825 (very full); vol. xvi. p. 
1017; vol. xvii. pp. 151, 175. 



m 

\^^m. Carpenter (Trans. A 

^K into classes as follows* 

I 

Calorimeters 



APPENDIX. 



699 



S. M. E., vol. XII. p. 825) divides calorimeters 



Condensing • 



Jet Condenser. 



Surface Condenser. . 



Direct determination of moisture 



I Hirn's Barrel or Tank. 

I Injector— continuous, 

[ Barr us— continuous. 
J Coil— continuous, 
j Hoadly Calorimeter. 
1. Kent— Tank Calorimeter.. 

( External— Barrus Superheating^ 

Superheating ■< " Universal. 

( Internal— Peabody Throttling. 

( Separator .- 
( Chemical. 

The barrel-calorinneter was first proposed by Hirn. A sample of steam 
is taken by a sampling nipple from the pipe and is led by a flexible hose 
into a barrel of water supported on scales. The weight and temperature 
of the water having been observed, a valve in the sampling pipe is opened, 
and a sample of the mixture passing through the pipe is drawn oft' and 
blown into the water until its weight increases an observed amount. The 
water being carefully stirred to equalize the temperature, its rise of tem- 
perature is observed. The percentage of water not evaporated into steam 
is then found by one of the following formulae: 

Let 1/ = heat-units per pound of steam in the mixture; 
A = " " *' " *' water " " '* 

TV = weight of the mixture added to the barrel ; 
X = weight of steam in this mixture; 
zv — X = " " water " " *' 

17 = total heat-units transferred to the water in the barrel. 



Then 



U= Hx^h{w - x). 



in which x is the only unknown quantity. 

If tables or formulae for the latent heat of steam are at hand (see note 
291) a simpler form of equation may be used. In this let t denote the heat- 
units per pound of condensed water added — which will be the difference 
between the sensible temperature of the steam at its original pressure and 
the final temperature of the water; let L denote the latent heat of the steam 
added. Then 

U= Lx -\- wt. 

For references on barrel-calorimeter see Trans. A. S. M. E., vol. vi. 
p. 288 ; vol. XII. p. 832; Whitham, Constructive Steam Engineering, page 
20; Power-Steam, September 1889. 

372. The headings for a boiler-test report, approved by a committee of 
the A. S. M. E. in 1885 and given in vol. vi, Transactions, p. 273. 

REPORTING THE TRIAL. 

XVII. The final results should be recorded upon a properly prepared, 
blank, and should include as many of the following items as are adapted 
for the specific object for which the trial is made. The items marked with 



700 



APPENDIX, 



a * may t)e omitted for ordinary trials, but are desirable for comparison 
with similar data from other sources. 

Results of the trials of a 

Boiler at 

To determine 



1. Date of trial 

2. Duration of trial 



Area. 



DIMENSION AND PROPORTIONS. 

Leave space for complete description. 

3. Grate-surface. .. .wide. .. .long . 

4. Water-heating surface 

5. Superheating-surface 

6. Ratio of water-heating surface to grate-surface. 

AVERAGE PRESSURES. 

7. Steam-pressure in boiler, by gauge 

*8. Absolute steam-pressure 

*9. Atmospheric pressure, per barometer 

10. Force of draught in inches of water 



*I2. 

*I3. 
14. 
15. 

16. 

17- 
18. 
19. 
20. 



23. 

24. 
25- 

26. 



AVERAGE TEMPERATURES. 

Of external air 

Of fire-room 

Of steam 

Of escaping gases 

Of feed-water 



FUEL, 

Total amount of coal consumed f 

Moisture in coal , 

Dry coal consumed 

Total refuse, dry pounds = 

Total combustible (dry weight of coal, Item 

18, less refuse, Item ig) 

Dry coal consumed per hour 

Combustible consumed per hour 



RESULTS OF CALORIMETRIC TESTS. 

Quality of steam, dry steam being taken as 

unity 

Percentage of moisture in steam 

No, of degrees superheated 



Total weight of water pumped into boiler and 
apparently evaporated % 



hours. 



sq. ft. 
sq. ft. 
sq. ft. 



lbs. 
lbs. 
in. 
in. 



deg. 
deg, 
deg. 
deg. 
deg. 



lbs. 
per cent 

lbs. 
per cent 

lbs. 
lbs. 
lbs. 



per cent 
deg. 



lbs. 



+ Including equivalent of wood used in lighting fire, i pound of wood equals 0.4 pound 
coal. Not including unburnt coal withdrawn from fire at end of test. 

X Corrected for inequality of water-level and steam.pressure at beginning and end of 
test. 



APPENDIX. 



7or 



27. Water actually evaporated, corrected for quali- 

ty of steam f 

28. Equivalent water evaporated into dry steam 

from and at 212° F.f 

*"29. Equivalent total heat derived from fuel in 
British thermal units f 

30. Equivalent water evaporated into dry steam 

from and at 212° F. per hour 

ECONOMIC EVAPORATION. 

31. Water actually evaporated per pound of dry 

coal from actual pressure and temperature f 

32. Equivalent water evaporated per pound of dry 

coal from and at 212° F. f , . . . . 

33. Equivalent water evaporated per pound of 

combustible from and at 212° F.f 

COMMERCIAL EVAPORATION. 

34. Equivalent water evaporated per pound of dry 

coal with one-sixth refuse, at 70 pounds 
gauge- pressure, from temperature of 100° 
F. = Item 33 multiplied by 0.7249 

RATE OF COMBUSTION. 

Dry coal actually burned per square foot of 

grate-surface per hour 

1 Per sq ft. of grate- 
Consumption of dry 1 surface 

coal per hour Coal ! Per sq. ft of water- 



35. 



^36. 



^38. 



#oR I assumed with one- | heating surface 



I 



sixth refuse, f 



I Per sq. ft. of least 
j area for draught . 

RATE OF EVAPORATION. 

39. Water evaporated from and at 212° F. per sq. 
ft. of heating-surface per hour 



lbs. 

lbs. 

. T. U. 

lbs. 

lbs. 
lbs. 
lbs. 



lbs. 

lbs. 
lbs. 
lbs. 
lbs. 



lbs. 



t The following shows how some ot the items in the above table are derived from 
others : 

Item 27 = Item 26 x Item 23 

Item 28 = Item 27 x Factor of evaporation. 

11 £ 

Factor of evaporation = — . //and h being respectively the total heat-units in steam 

of the average observed pressure and in water of the average observed temperature of feed^ 
as obtained from tables of the properties of steam and water. 

Item 29 = Item 27 x (//— h). 

Item 31 = Item 27 -s- Item 18. 

Item 32 = Item 28 -f- Item 18, or = Item 31 x Factor of evaporation. 

Item 33 = Item 28 -^ Item 20, or = Item 32 -^ (per cent 100 — Item 19), 

Items 36 to 38. First term = Item 20 x -. 

Items 40 to 42. First term = Item 39 x 0.8698. 

T 1 Item 30 

Item 43 = Item 29 x 0.00003, o^" = ""• 

34i 

Difference of Items 43 and 44 

Item 45 = 22 22. 

Item 44. 



702 



APPENDIX. 



-40. 



^42. 



f Water evaporated 
j per hour from tem- 
j perature of 100° F. 
into steam of 70 
pounds gauge-pres- 
sure. f 



Per sq. ft. of grate- 
surface 

Per sq. ft. of water- 
heating surface. . . 

Per sq. ft. of least 
area for draught . 



COMMERCIAL HORSE-POWER. 



43 



On basis of thirty pounds of water per hour 
evaporated from temperature of 100° F. into 
steam of 70 pounds gauge-pressure ( = 34^ 

lbs. from and at 2i2°)f 

Horse-power, builders' rating, at. . .square feet 

per horse-power 

45. Per cent developed above, or below, rating f. 



44 



lbs. 
lbs. 
lbs. 



H.P. 



H.P. 

per cent 



t See note on preceding page. 

For other and more extended headings see Trans. A. S. M. E., vol. xvi. 
pp. 962 and 990, No. 650. 

374. See Flather, J. J., Dynamometers and Measurement of Power. 
Consult also Trans. A. S. M. E., vol. iv. p. 227 ; vol. vii. pp. 274, 550; 

vol. IX. p. 213 ; vol. X. p. 514 ; vol. xi. p. 959 ; vol. xii. pp. 694, 700; vol. 
XIII. p. 497 ; vol. XIII. p. 531 ; vol. xvi. p. 806. 
See also Electrical World, Sept. 17, 1887. 

375. For the indicator, consult Whitham, Const, Steam Eng'g, pp. 136 to 
221 ; Thurston, Manual of the Steam-engine, Part II, pp. 664 to 684 ; Thos. 
Pray, Twenty Years with the Indicator ; F. W. Bacon, Treatise on the 
Hichards Indicator ; Chas. T. Porter, The Steam-engine Indicator , F. F, 
Heminway, The Steam-engine Indicator ; Geo. H. Barrus, the Tabor Indi- 
cator. 

Also, Trans. A. S. M. E., vol. v. p. 310 ; vol. vii. p. 489 ; vol. ix. p. 293 ; 
vol. X. p. 586 ; vol. XV. pp. 277, 45 

For friction of engines, see Trans. A. S. M. E., vol. viii. p. 86, vol. 
X. pp. no, 392. 

377. For friction.of shafting in mills, see Trans. A. S. M. E., vol. vi, p. 
461 ; vol. vii. pp. 138, 265, 449. 

378. For electric motors in shops, see Amer. Engineer and R. R. Journal, 
T894, p. 165 ; Ibid., 1895, p. 113. 

For gas-engine and subdivided power, see Power, May, 1895. 

382. For fire-protection of mills, see Trans. A. S. M. E., vol. 11. p. 301 ; 
-vol. XI. p. 271 ; vol. IV. p. 399. 

See also circulars of Manufacturers' Mutual Insurance Co. for slow- 
fcurning mill-constructions. 



INDEX, 



PAGE 

A frame of vertical engine \ 271 

Absorption dynanaometer , 663 

Accidents in engine-room 657 

Acid test for oils 657 

Action of curving rolls 383 

steam in compound engines 118 

Adamson ring for flues 442 

Agincourt, engine of 27 

Air cooling of injection-water 98 

compressor, back-acting, Rand's 29 

pump and foot-valve 99 

space in grates 523 

valves 310 

Allan link-motion 228 

Alarm for low water 589 

Allen link-motion 232 

sectional boiler 468 

resistance governor 260 

valve 192 

Alignment of foundation-template 280 

outer pillow-block or outboard bearing 283 

Almy boiler 499 

American mechanical stoker 534 

Analysis of a power plant 3 

Angstrom valve-gear , 231 

Annealing of steel boiler-plate 377 

Apparatus for drawing motion-curves 176 

Armington & Sims piston-valve 196 

shaft-governor 256 

Arrangement of a power plant ... 674 

rings in boiler-shells 383 

rivets in a joint 400 

Artificial draft 551 

Asbestos packings 308 

Ash-pit in boiler-settings 518 

doors in boiler-settings 511 

Attached air-pump 99 

703 



704 INDEX, 

PAGE 

Automatic cutoflf engine 14S 

dam per- regulator 54^ 

stokers 530, 692 

water-feeding apparatus 60& 

Auxiliary engine for valve-motion of pumps , 218 

Babcock & Wilcox engine-governor 252^ 

engine with steam-thrown valve 219 

feed- water filter 627 

mechanical stoker 531 

sectional boiler 461 

Bache, test of 682 

Back-acting engine 23 

of H. M. S. Agincourt 27 

S. S. Belle 25 

Back connection 545. 

Bacon's trunk-engine 22^ 

Backward engine 15, 

Balanced engine, Durf ee's 680 

, Wells' 69 

governor , 243. 

governors 253. 

slide-valves 193, 685 

Balancing of engines 274 

Baldwin locomotive fire-box -. 483 

Baldwinsville rotary pump 56 

Ball Engine Co. tandem compound 121 

Balloon boiler 371 

Banking fires of boilers 617 

Baragwanath feed-water heater 604 

Bates-Corliss cylinder and valve-gear 2i8 

engine bearing 339 

engine cross-head 316 

tandem-engme foundation 277 

Bay City Iron Works, upright boiler 493 

Beam compound engine 125 

Beam-engine of steamer, Francis Skiddy 44 

engines 42 

engines of U. S. cruiser Chicago 46 

Bearings, lubrication of 651 

Bed or frame of a vertical engine 271 

Bed-plate of a horizontal engine 265 

Belle, engine of 25 

Bellerophon, engine of 24 

Belpaire fire-box 415, 489 

Bent-tube sectional boilers 468 

Berry man feed-water heater 607 



INDEX. 705 

PAGE 

Bethlehem rolling-mill engine 33 

Blast-furnace boiler 435 

Blisters in boiler-plate 376 

Blowing-engine, back-acting 28 

Blow-off valve 610 

Bogie cross-head guides 312 

Boiler explosions 639 

fronts 510 

heads 385 

inspection 637 

, locomotive 482 

management 616 

, marine. 477-479 

of steamer Bergen 479 

Orange 48 1 

plate, curving of 380 

punching-press 391 

, steel 376 

, testing of , 378 

, thickness of 378 

, wrought-iron 374 

patches 635 

repairs « 635 

rupture 640 

scale 620, 695 

sectional 451 

, internally fired 498 

setting 504 

, shapes of 370 

shell with few joints 384 

shells, joints in 387 

test for efficiency. 660, 698 

tubes 445 

Boilers, corrosion of 63 f 

, classification of 421 

, deterioration of 629 

, grooving of 630 

internally fired , 471 

, overheating of 629, 695 

, unequal contraction of 630 

expansion of 630 

, wear and tear of. 629 

Bolts for engine-foundation 278 

Boring of cylinder , 288 

Boston pumping-engine fly-wheel. 347 

Bourdon gauge for boiler 578 

Bowling rings for flues 442 

Box-piston 293 



7o6 INDEX. 



PAGE 



Braces, see Stays. 

Bramah rotary engine 58 

Brasses of connecting-rod 323 

Breeches boiler 474 

Bridge-wall 538 

Brown valve gear 231 

Buckeye engine bed plate , , 270 

engine valve igi 

Buck-stays 505 

Built-up crank 334 

Bulkley gravity or siphon condenser 107 

Bull Cornish pumping-engine 74 

ring..- 299 

Bump-joint for flues 439 

Bursting pressure for boilers < 688 

Bushing for stub end - 325 

Biiss-governor 252 

Butt-joint 403, 404 

B valve 163 

By-pass valve for compound engines. . . /. 353 

Cahall water-tube boiler 459 

Calibration of steam-gauge 581 

Calorific power of a fuel 557 

Calorimeter test for quality of steam - . . 662, 698 

Cam and release valve-gear 204 

riveting-machine 397 

Card from indicator 666 

Care and management of boilers 616 

Case oscillating engine 20 

Cast-iron crank 331 

for boiler material <. 373 

grates 521 

packing-rings 298 

Cataract of Cornish engine 75 

Caulking of boiler-seams 419 

Centre-crank engine .... 15, 329 

Centrifugal circulating pump 102 

governors 243 

separator for steam-pipe 359 

Chain grate 530 

Challenge reversible rotary engine 57 

Charcoal-iron in boilers 375 

Check-valves on feed-pipes 593 

Chimney ' 549 

Circulating-pump 102 

Classes of sectional boilers 455 



INDEX. 707 

PAGE 

Classification of boilers by type 421 

«ngines by use of steam 70 

governors 243 

Clayton air-compressor 16 

Cleaning fires of boilers 617 

the heating surface of boilers 618 

Closed stoke-hole 551 

stub end 323 

Closed tube sectional boiler 464 

Coal per horse-power per hour 562, 563 

square foot of grate , 560 

Cold-water test of boilers 638 

well 97 

Collar-bound bearing . 339 

Colt or West disk-engine 66 

Column-pipe for water-guage 584 

Coil-boiler 498 

Combination horizontal and vertical engine 40 

Combustion, air for , 567 

chamber ... 541 

in locomotive boiler 485 

, heat of 560 

per square foot of grate 560 

Compensators in non-fly-wheel pumps 136 

Composite band-wheels . 348 

Compound engines 117 

locomotives 137 

rotary engine , 61 

Compounding above atmosphere 134 

without condensation 134 

Compressed air for transmitting power 670 

Compression as a method of governing ,. . 683 

in the steam-cylinder 166 

Concave calking 419 

Concrete foundations 276 

Condenser of a condensing engine 91 

Condensing and non-condensing engines 85 

Conditions for use of cylinder-boilers , 433 

tubular boilers 449 

Conical pendulum-governor 245 

Connecting-rod 320 

Connections of the governor to control the engine , 264 

Concentrated or subdivided steam-power 668 

Construction of a power house 673 

riveted joint 390 

engine-foundations 275 

Continuous-expansion engines , 116 

Control of energy in steam-engines 144 



70J5 INDEX, 

page: 

Cooper, horizontal engine , \% 

Copper as boiler material 371 

steam-pipe 353; 

Corliss pumping-engine, Pawtucket 50 

valve-gears 211 

Cornish pumping-engine of Brooklyn Water-works 74, 75 

Corliss steam-jacket joint . 292: 

upright boiler. — 494. 

Cornish boiler 473 

Corrosion of boilers 631 

Corrosion of steel boiler-plate 37S 

Corrugated flues and furnaces 4777 

pipe for expansion, Wainwright's 354 

Counterbore in the cylinder 289. 

Counterweighted crank 332: 

Coxe chain-grate 530 

Cracking of steam boiler-plate , 377 

Craig pump-condenser 114. 

Cranked axle 334. 

Crank end of cylinder 13 

pin 330- 

pin oiler 654 

shaft 329- 

Cross-compound engine , 124. 

head 314 

head pin 319. 

Crown-bars 414 

sheet stays .... 415 

Cup leather packing 297° 

Curved-tube sectional boilers 468- 

Curving boiler-plate 380- 

Cushioning in a steam-cylinder , 166- 

Cut-off defined 82: 

engines 147 

governors. 243 

varies by varying angular advance of eccentric 239. 

lap of valve 236 

point of release or trip 240^ 

throw of valve 200 

Cylinder boiler. c . . . . 422 

casting 287 

cocks 290 

cover t 288 

flue boiler • 439^ 

in multiple-expansion engines, arrangement of, 131 

jacket 29O' 

tubular boiler 444 

of Worthington-Corliss engine 212 



INDEX, 709 

VAGB 

Cylindrical marine boiler 477 



Dake square-piston engine 64 

Dallas, tests of 682 

Damper in chimney-flue 548 

regulator 548 

Dashpots of Corliss valve-gear 214 

Dead-centres of engine 13 

plate of furnace 516 

Dean beam pumping-engine 49 

De Laval steam turbine 64 

Design of a riveted joint 399 

slide-valve 181 

Deterioration of boilers 628 

Diagonal engine, see Inclined. 

Diagram of compound engine 116 

condensing and non-condensing engines 86 

effort in a cut-off engine 148 

throttling-engine 147 

showing loop 151 

expansive working 82 

non-expansive working. 81 

triple engine 130 

Woolf compound engine 128 

Diaphragm steam-gauge 579 

Differential governors 244 

Direct-acting engines 41 

pump for boiler-feed 596 

vertical engine: 36 

Disengagement area 424 

governors 244 

Disk-crank 332 

engine 61 

valve 351 

Distribution of power by gas, electricity, or air 670 

Doane exhaust-head .... 365 

Domes for boilers 426 

Double- and single-acting engines 73 

crank 330 

connecting-rod 327 

Cornish boiler 473 

ported valve 193 

riveted joint 402 

Down-draft furnace 574 

Dow steam turbine 62 

Dudgeon's tube-expander 447 

Dumping-grates 524 



7IO INDEX, 

PACK 

Dunbar packing , 301 

spray boiler 470 

Duplex injector condenser no 

Durfee's piston-packing 300 

Drainage of steam-pipe 357 

Draft, artificial 551 

Drift pin 406 

Drilling of boiler-plate for rivet-holes 390 

Drip-connections 368 

Dry pipe in boilers 431 

D valve 157 

Dynamic equivalent of a heat-unit 4 

Dynamometers 663 

Dynamometric governors 262 



Eccentric 340 

fittings for steam-pipe 357 

is a crank 159 

rod 341 

strap , 340 

Eclipse exhaust-head 365 

ref rigerating-machine 41 

Economic boiler 489 

Economy of heating feed- water 603 

Economizers 605 

Edge planing of boiler-plate 419 

Edmiston oil-filter , 365 

Efficiency defined 83 

Egg-ended boiler 371 

Ejector condenser with pump 109 

Electrical distribution of power. , 670 

Electromagnetic governors 261 

Electromotive force liberated from fuel i 2 

Elephant boiler 434 

Energy resident in hot water 642 

Energy, sources of i 

Engine constant in horse-power formula 9 

foundations and bed-plates 265 

lubrication 649 

management 645 

Equilibrium-valve of Cornish engine 74 

Ericsson vibrating engine 65 

Errors of indicator 666 

Evaporation per square foot of heating-surface 566 

Exhaust clearance 167 

heads 365 

lap 166 



I 



INDEX. 711 

PAGE 

Exhaust pipe 363 

steam ejector condenser 11 1 

heaters > 603 

Expanding of tubes 446 

Expansion of boilers 509 

joints for steam-pipe 354 

Expansion valve-gear 184 

Expansive and non-expansive working of engines 79 

Explosions of boilers 639 

Extension-fronts in boiler-settings 511 

External fire-box for boilers 572 

Externally-fired boilers 42s 

sectional boilers 451 

Extractors for oil , 365 



Failure of a riveted joint 405 

Fall River Steamboat Co. inclined compound engine 0. . . . 127 

False seat for valve , 239 

Farcot governor. ... 250 

Feathering paddle-wheels 38 

Feed-pipe ". , 592 

pump of condensing engine 115 

pumps for boilers 593 

water, filtration of 626 

heating 603 

introduction of 591 

purification of 626 

valves 592 

Ferry-boat engine without walking-beam 36 

Fibrous packings 296 

Field tubes 464 

Filters for oil , 365 

Filtration of feed- water 626 

Fink link-motion 232 

Fire-box iron for boilers 375 

brick arch for locomotive-boilers 486 

doors in boiler-settings 512 

engine boiler 495 

, rotary 55 

Fire protection of a power plant 675 

Firing of boilers 616 

Fishkill Landing Corliss engine 213 

Fixed pressure-plate system of Atlas engine 197 

Flange iron for boilers 375 

Flanging of heads 385 

Flexible expansion-joint 355 

plate balancing system 201 



712 INDEX, 

PAGE 

Flexure of butt-joint 403 

lap-joint. 3go 

Float water-gauges 588 

Floors of a power plant , i 675 

Flue brushes and scrapers. , 619 

Flue boiler ^ 439, 690 

doors in boiler-settings , 512 

gases, quality of , 661 

heaters 605 

Flue to chimney 546 

Flush fronts in boiler-settings. 511 

Fly-bail or conical pendulum governor , 245 

Fly band-wheels 348 

Fly-wheel 342, 687 

pump for boiier-feed 595 

Footings for engine-foundations 276 

Foot-valve of air-pump 99 

Force resident m one pound of fuel , 559 

Forced draft 551 

Fore-and-aft compound engine 124 

Forged crank 334 

Forked connecting-rod . 327 

Forward-running engine 15 

Foundation-bolts 278 

Foundations for engines 265, 273 

Foundation template 279 

Free expansion in compound engine 128 

French boiler *. ..^ 434 

Front connection 546 

Friction of slide-valves 194 

Fritz piston-packing ^ 301 

Fuel-oil under boilers 567 

, source of motor energy 2 

Full fronts in boiler-settings , ; . . . . 510 

Fuller's marine-engine governor 264 

Furnace in boiler-settings 520 

Fusible plugs ; 590, 694 



Gab-hooks ■ 222 

Gallatin, tests of 682 

Gallows-frame of beam-engines 44 

Galloway boiler 474 

Gang-drill 392 

Gang or multiple punch 392 

Gardner spring-governor. 255 

three-cylinder trunk-engine 67 

Gas as fuel 570 



INDEX, 713 

PAGE 

Gaskets for steam-pipe 352 

Gaskill or Holly inclined pumping-engine 40 

Gaskill pumping-engine 48-51 

Gauge-cocks 587 

Geared fly-wheels 349 

Gib and key for connecting-rod 323 

Gibs for crosshead , 315 

Giddings engine-valve 202 

Girder bed-plate section 269 

Gland in stuffing-box 306 

Glass water-gauge 583 

Gooch link-motion 227 

Gonzenbach two-valve gear 186 

Gordon & Maxwell cataract-cylinder 76 

Governors for steam-engines 241 

Grading of steam-pipe 356 

Graphite as a lubricant 652 

Grate-bars in boiler-settings. 521 

Grate and heating-surface 565 

Gravity as motor force 2 

Gravity condenser , 105 

separator for steam-pipe 360 

Grease-cups 655 

Green economizer 605 

Greene valve-gear > . ... 211 

Gridiron slide-valve 192 

Grooving of boilers 630 

Grouping of cylinders in multiple-expansion engine 132, 133 

Guides for slides 311 

Gusset-stays 413 



Hackworth valve-gear 231 

Half-blind hole 393 

Half-fronts in boiler-settings 511 

Hammer test of boilers 639 

Hand-holes 419 

riveting 395 

Hanging of boilers. , 508 

steam-pipe > 356 

Harrison boiler 456 

Hawley down-draft furnace 575 

Haystack boiler 371 

Heating of bearings 657 

Head end of cylinder 13 

Heads of boilers 385 

Heat of combustion 560 

Heating-surface and grate-surface 565 




714 INDEX, 

PAGE 

Heat, transfer of 564. 

unit, dynamatic equivalent of 4 

Heine sectional boiler 467 

Herreshoff water tube boiler 502 

Heusinger von Waldegg gear 230 

High-speed engines 70 

Hicks four-cylinder trunk-engine 6S 

Historical summary 67 y 

Hollow bridge-wall , 535 

piston- valve 196 

Hoppes feed- water heater 603. 

Horizontal engine 26 

grates 535 

separator for steam-pipe 36 1 

tubular boiler 444 

sectional boiler 460 

Hornblower compound engine , . . . 12a 

Horse-power of a cylinder 7 

defined 4. 

in metric units 4 

nominal 5 , 679 

of the resistance 8 

Hot-water test of boilers. 638 

Hot- well 114 

Houston, Stanwood & Gamble cross-compound engine 126 

18-flue boiler 443 

Hungarian street-railway power-plant engine ... 32 

Hunting of engine-governors 242 

Huntoon resistance governor . . . 260 

Hunt stub end 326 

Z-crank engine 66^ 

Hydraulic reversing-gear. 234 

riveting-machine 397 

Hydrostatic test of boilers 638 



Inclined-cylinder beam-engine 47 

Inclmed engine 36 

grates i 535 

Incrustation or scale in boilers 620 

Ide breaking- cap 291 

engine cross-head 316 

Independent air-pump 103 

Inertia-governors 243, 256 

Indicator 664 

Injection defined 91 

, weight of 68a 

Injector 599^ 



INDEX, 715 

PAGE 

Injector condenser 106 

I section for connecting-rod 325 

Inside lap 166 

Inspection of boilers 637 

Intermediate cylinder defined 117 

Intercepting-valves in compound locomotive I3i^ 

Internal condensation and re-evaporation defined 84, 683 

Internally-fired sectional boilers 4q& 

shell boiler 471 

Introduction of feed- water 591 

Inverted vertical engine 33 

Isochronous governing 242 



Jet condenser of steamer Fiancis Skiddy 92 

Joint of bed-plate and foundation 282 

Joints in boiler-shells , 387 

of surface-condenser tubes 95 

Jones mechanical stoker 534 

Joy valve-gear , 69, 229 

Junk-ring, 294 



Kennedy spiral punch for boiler-plate 392 

Key and coiter for connecting-rod 323 

Keys for crank 331 

Kilowatt defined 5. 

Knock or pound in engine-bearings , 658 



Lagging the cylinder 292 

La France rotary engine . . , 55 

Laketon tandem oil-pumping engine 136 

Lamination in boiler-plate 376 

Lancashire boiler 473 

Lane & Bodley connecting-rod 324 

cross-heads 315 

outboard bearing 285 

Lane steam-gauge 580 

Lap in slide-valve 1 64 

Lap-joint with cover-plate 403 

Lap-riveted joints 401, 402 

Leavitt beam-engine (Lawrence) 47 

Leavitt, Calumet and Hecla, butt-joint 405 

steam jacket-joint 292 

Lead in the slide-valve 168 

varies in Stephenson link-motion 227 

Leakage-grooves in pistons 297 



7l6 INDEX. 

PAGE 

Lee exhaust-head 365 

Length of engine 17 

Lever riveting- machine 397 

safety-valve 613 

Lidgervvood reversible rotary engine 57 

Limitations of the single slide-valve 183 

Lyman exhaust head , 365 

Link-motion for riding cut-off valves 233 

of Stephenson or Howe and others 223 

Loaded governors 247 

Locating the bed- plate on the foundation , ,. 281 

Location of a power plant 671 

Locomobile engines 144 

Locomotive boiler 482 

crank 334 

reverse gear of P. R. R 224 

Long cylinder-boilers, hanging of 510 

Low-speed engines 71 

Low-water alarm 589 

Lubrication of the engine. , 649 

Lugs for hanging boilers «....,.««««!.«..«,.. 508 



McEwen double piston -valve 195 

McNaught engines = 125 

Machme-riveting 395 

Magazine feeding-apparatus , 608 

Main bearing ... 337 

Malleableized iron in boilers , 374 

Management of boilers. , 616 

engines 645 

Manholes 416 

Manning boiler ^ . , 491 

Marden down-draft furnace .'. 576 

Marine boiler 477 

connecting rod 326 

crank-shaft. 335 

cylinder relief valve 291 

engine-governors 263 

triple open-frame, engine 34 

Marshall valve-gear 231 

Martin boiler 478 

Mass of engine foundation 274 

Materials for boilers 371 

Mattes connecting-rod 326 

Mead & Dick inertia governors 257-259 

Mechanical grates 529 

stokers 530 



INDEX, 717 

PAGE 

Mechanism of compound engine 120 

engine 7, ii, 679> 

Meyer riding cut-off 185 

Metallic packings 307 

Meyer cut-off valve 237 

Milwaukee, Allis inverted vertical pumping-engine 35 

Mississippi gauge-cock 588- 

Modifications of locomotive-boiler 483. 

Monadnock monitor engine 53 

Monarch boiler 488' 

Monitor half-beam engine 53 

Morton ejector condenser iii, 682 

Motion -curves for slide-valves 172 

Motor energy, sources of i 

Mouthpiece of boiler-furnace 516 

for manholes 418 

Mud-drum 437 

Multiple-expansion engines 117 

rivet butt-joint 404. 

Murdoch long valves 190 

Multiported valve seat. 193. 

Multitubular boiler 444 



Napier connecting-rod 326 

Nasmyth test for gum in oils 656 

Nominal horse-power 5, 679> 

Non-condensing engines 8 

Non-conducting coverings for steam-pipe , 362, 688- 

Non-expansive working of engines 81 

Non-fly-wheel pump 5^5. 

Nozzles for manholes 418. 



Oil as fuel 567 

Oil-cup lubric/»tor 653. 

Oil-extractors 365 

Oil-filters 365. 

Open-frame engine 69- 

Open-stub end 323. 

Orsat gas-analysis apparatus 662 

Oscillating engine 17 

paddle-engine 19, 

Outboard bearing, alignment of 2^y 

Outer pillow-block, alignment of 283 

Output of a power plant ^ 

Outside lap 164, 

Overheating of boilers 629, 695 



71 8 INDEX. 

PAGB 

Packings for piston-rods 306 

Paddle-wheel engine of L. B. & S. C. Ry 38 

Parallel motions 319, 687 

Parabolic governor 249 

Parsons steam turbine , 63 

Patches on boilers, 635 

Payne Corliss engine 217 

Pendulum engine -. 65 

Pennsylvania R. R. locomotive link-motion 224 

Perforated dry pipe 421 

Phosphorus in boiler- plate 377 

Pickering s spring-governor 253 

Pierce rotary boiler 470 

Pin-drill-for tube-sheets. 446 

Piston-packings 295 

rings 297 

rod 303 

speed 72 

structure of ,..., 293 

valve 194 

Pitman in beam-engines 42 

Pitman 320 

Pitting of boilers. c . . . 634 

Plain cylinder-boiler 422 

slide-valve working full stroke , 157 

Plate piston 294 

Polar diagram for slide-valves 176 

Polonceau link-motion 233 

Poppet-valves , 202 

Pop safety-valve 614 

Portable engines 144 

Porter- Allen pressure-plate system 200 

two-valve gear 187 

Porter steeple compound engine 123 

Position governors 244 

Pounds of air per pound of coal 567 

coal per square foot of grate 560 

water per horse-power per hour 563 

pound of coal 562 

Power house, construction of 673 

plant arrangement of 674 

, fire protection of 675 

, floors of 675 

, location of , ... 671 

reversing-gears 233 

Preheating feed-water 603 

Pressure-plate to balance slide-valve ig6 

Prevention of boiler-scale. 625 



INDEX, 719 

PAGE 

Previous purification of feed-water 626 

Priming of boilers 424 

Proportions of compound-engine cylinders 142 

slide-valve 158 

Prosser tube-expander 447 

Pump condensers 112 

governor ^ 258 

lubricators 650 

Pumping-engine, Corliss 50 

Dean 49 

direct vertical type 37 

Gaskill horizontal beam 48 

Leavitt, Lawrence 47 

Punching and drilling compared 392 

Punch and die for boiler-plate 392 

Punching of plate for rivet-holes. 390 

press for boiler-plate, Hilles & Jones 391 



Quadruple-expansion engines. 117 

Quarter-boxes 337 

Quartering cranks 17 

Radial valve-gear 228 

Ransom gravity or siphon condenser 106 

Rates of combustion per square foot of grate 561 

Ratio ot grate- surface to heating-surface 565 

Reaction in boiler-explosions 643 

Reaming of holes for rivets , 394 

Receiver in compound engine 124, 135 

Reciprocating steam-engine, parts of 9 

Recording-gauge 582 

Rectangular marine boiler 480 

Reduced compound-engine diagram. , , 129 

Re-enforced domes for boilers 427 

Re-evaporation defined 84, 683 

Re-heater in compound locomotive 138 

Re-heaters for compound engines 131 

Regulation of boiler-fires 618 

Releasing-valve gears. 210 

Relief -valves in the cylinder , 290 

Removal of boiler-scale »623 

Repairs to boilers. 635 

Resistance governors 258 

Reynolds upright boiler 495 

Retarders in boiler-tubes , ,. . . . 446, 692 

Reversing-valve gears . 220 

Ribbed lubes for boilers 446 



720 INDEX. 

PAG& 

Richardson locomotive balanced valve 198 

Rider automatic cut-off with trapezoidal ports 238 

, inclined engine 39, 

Riding cut-off 185 

Refined iron in boilers 375. 

Riveted joint, design of 399 

, failure of , 405 

, strength of 399, 689 

joints for boiler-shells 389 

Riveting of piston-rods 304 

Robertson exhaust-head 365 

Rocking grates 528 

valve cam 205 

Rockvvood compound engine 143. 

Roller bearings for valves 202 

Rolls for curving plate, Hilles & Jones 382. 

Root sectional boiler 462 

trunk-engine 21 

Roney mechanical stoker 533 

Rotary steam-engine 52^ 

Running of engines 645 

Rupture of boilers 640 

Rush, tests of 682 



Safety-plugs 59a 

stops 262^^. 

valve 612, 694 

water-gauge 58s 

Scale clogging feed-pipes 592 

in boilers 620 

Scotch marine boiler 477 

Schutte exhaust steam-condenser 112 

Seacock for marine-engine condenser no 

Sectional boilers 451 

internally fired 498 

coverings for steam-pipe 363 

Segmental fly-wheels 345 

Sellers hydraulic riveting-machine 397 

steam riveting-machine ... 396^ 

Semi-portable engines 144 

Separators for oil 365 

steam-pipe 359 

Serve-tubes for boilers 44^ 

Setting of non -expansive slide valve • 161 

valve by indicator 17^ 

sound 170 

trammel > 171 



I 



INDEX. 721 

PAGE 

Shaft-bearing , 338 

Shati-governors .... 244, 255 

Shaft of marine engine 336 

Shaking-grates 525 

Shapes of boilers , 370 

Shell boilers, externally fired 421 

internally fired. .. 471 

Shims in aligning engines 282 

Shortening steam passages , , . . 189 

throw of a valve 19I 

Shrinkage of pistons 304 

Sickles cut-off 210 

Side cam 206 

crank engine ......< 15, 329 

lever engine , 49 

Sight-feed lubricators o 650 

Silsby rotary engine , . 55 

Simple and continuous-expansion engines . . . = , 116 

Single acting rotative engines » 77 

riveted joint 401 

slide-valve, limitations of 183 

Siphon condenser 106 

Slides or guides 31?! 

Slip ioint for expansion in steam-pipe 354 

Slipper cross-head 69 

Smoke-prevention 573, 693 

Snifting-valves in the cylinder 290 

Soil, supporting power of 273 

Solid fly-wheels. 345 

Spherical-unit sectional boiler. . , 457 

Spider piston . . , *.;......... 293 

Spiral riveted pipe 364 

Spindle-governors. 244 

Spring-governors 253 

Square-piston engine : 61 

Standardization of steam-gauge 581 

Stationary grates 520 

Starting an engine 645 

Staying of domes 432 

tubular and flue boilers 449 

Stays and staying , 407 

Stead's water-tube boiler 470 

Steam-boilers, see Boilers. 

Steam-chimney 478, 482 

drums for boilers 425 

gauge for boiler 578 

jacketing 290 

jacket for valve-chest 195 



12.2 INDEX. 



PAGE 



Steam-jet cleaners Oig 

packing 301 

pipe 351 

pressure-test of boilers 638 

reversing-gear 234 

Steam riveting-machine 3g6 

thrown valves 216 

space in boilers 425 

turbine 61 

Steam-loop for draining steam-pipe 361 

Steel boilers 376 

crank 332 

Steeple compound engine 123 

Steidlen loaded parabolic governor 251 

Step grates 527 

Stephenson link-motion 223 

Stern bearing for marine shaft 338 

Stevens cut-off for river-boat engines 207 

Stiffening-rings for flues , 441 

Stirling boiler •• 458 

Stokers, mechanical 530 

Straight-line engine 272 

slipper cross- head 313 

Strains in fly-wheels 344 

Strap of eccentric 240 

Strength of a riveted joint 399 

Stub end 321 

Structure of beam-engines 43 

the piston 293 

Stuffing-box - 305 

Subdivided steam-power 668 

Superheating 291 

Supporting power of soils 273 

Surface condenser 93 

Sweet pressure-plate 201 

Tandem compound engine 121 

Tangye or Porter bed-plate 270 

Tank bed-plate 267 

Testing boilers for efficiency 660, 699 

of boilers for strength 638 

boiler-plate 378 

the power plant for efficiency 660, 699 

Tests of lubricants 656 

rivets 400 

Theory of boiler explosions » 642 



INDEX. 723 

PAGE 

Theory of the fly-ball or Watt governor 246 

Thickness of boiler-plate 378 

Three- and four-valve gears 188 

Three-furnace boiler 476 

Three-way and four-way cock- valves 1 54 

Thornycroft water-tube boiler 501 

Throttling engines 145 

governors 243 

Throttle valve 146, 35a 

Through-stays 408 

Thrust-bearing , . 336 

Tie-rods for boiler- settings 505 

Tit drill for tube-sheets 446 

Tram mel for valve-setting 162 

Transmitting dynamometer 663 

Transfer of heat 564 

Trapezoidal ports for cut-off valve 237 

Traps for drainage of steam-pipe 358 

Travel of slide-valve 159 

Travelling grates c 257 

Trip-valve gears r 210 

Triple crank 330 

expansion engines 117 

engine diagram 130 

riveted joint 402 

Throw of slide-valve 159 

Trunk-engine, Bacon's 22 

Gardner's 67 

Hicks' 68 

of H.M.S.Bellerophon 24 

Root's 21 

Westinghouse 78 

Try-cocks for water-level 587 

Tube-cleaners 619 

Tubular boiler 444 

Tube-joints for surface condensers 95 

Turbines, steam 61 

Twiss engine with loaded governor 248 

Two-flue boiler 44a 

valve engines 184^ 



Unequal contraction of boilers 630- 

expansion of boilers 630 

Union boiler 4341 

Pacific R. R. boiler 484. 

Units of output in a power plant 4 



724 INDEX. 

PACK 

Upright boiler • 491 

Use of Zeuner polar diagram. . . . » 180 

U. S. cruiser Maine, independent air- and circulating-pump 103 

Valves and valve-gearing 153 

balanced by counter-pressure 201 

Valve-chest location 289 

gear for high degrees of expansion 184 

problems and design 181 

stem 341 

Valves taking steam internally = 201 

Variable cam ; 206, 209 

cut-off engine 147 

valve-gears 235 

Velocity of steam in pipe and ports 159 

Vertical engine 31 

frame or bed 271 

tubular sectional boiler 460 

Vibrating piston-engine 64 

Vibration of engine-foundations 275 

V hooks 223 

Victor reversible filter 628 

Wagon-boiler 422 

Wagon-top locomotive boiler 483 

Wainwright's feed-water heater 606 

Willans' single-acting central-valve engine 80 

Walschaert valve-gear 230 

Walters pendulum or vibrating engine 65 

Ward water-tube boiler 501 

Wear and tear of boilers 629 

Wasting of boiler-plate 634 

Water evaporated per pound of coal 562 

gauge for boiler 582 

grates 524 

leg front for boiler-settings 516 

per horse-power per hour 563 

pocket for draining steam- pipe 359 

space in boilers 425 

Waters' spring-governor 253 

Water-tube or coil boiler 498 

Watertown engine bed-plate. ... . - 267 

rotary engine 58 

tandem compound engine 122 

variable cut-off gear 237 

Watt governor 245 

Welding of boiler-joints 388 



INDEX, 725 

PAGE 

Wells balanced engine 69 

Westinghouse compound single-acting engine 137 

relief-valve 291 

single-acting engine 78 

Wetherill-Corliss engine 268 

Wharton-Harrison boiler 456 

Wheeler's feed-water heater 606 

Wheeler surface condenser 94 

Wilkinson mechanical stoker 532 

Winans locomotive cam 206 

Wipers for river-boat engines 207 

Woodbury engine connecting-rod 325 

cross-head 318 

pressure-plate system 199 

Woolf compound engine 120 

Wooton fire-box \,.. 485, 487 

Worthington's ejector condenser 109 

self-cooling condenser 100 

Wright spring-governor 255 

Wrist-plate of Corliss valve-gear 214 

Wrist-pin 319 

Wrought-iron boilers 374 

grate bars 523 



Yoke for valve-cam o . . . 205 

Yoked piston-rod for crank-motion . . . = 16 



Zell sectional boiler, details t 463 

Zeuner polar diagram for slide-valves <. 176, 683 



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